<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with Wdesk from Workiva-->
<!--Copyright 2022 Workiva-->
<!--r:29a4b4dc-8cca-4a2c-8b00-1653a7b25685,g:4140688d-8727-4745-9ca5-400c87633167-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://www.nektar.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFOPERATIONS" xlink:type="simple" xlink:href="nktr-20220630.xsd#CONDENSEDCONSOLIDATEDSTATEMENTSOFOPERATIONS"/>
  <link:definitionLink xlink:role="http://www.nektar.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFOPERATIONS" xlink:type="extended" id="iaf72d627cb5e4fc590a2ffb4fbe2309e_CONDENSEDCONSOLIDATEDSTATEMENTSOFOPERATIONS">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_620b285c-c288-4516-b9e8-7f356df3c1bf" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenuesAbstract_a6153d7d-58b9-4871-833b-62bbb878dbfc" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RevenuesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_620b285c-c288-4516-b9e8-7f356df3c1bf" xlink:to="loc_us-gaap_RevenuesAbstract_a6153d7d-58b9-4871-833b-62bbb878dbfc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_3dd9e5ef-a69d-4182-889c-ba9781fd1a8e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_a6153d7d-58b9-4871-833b-62bbb878dbfc" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_3dd9e5ef-a69d-4182-889c-ba9781fd1a8e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostsAndExpensesAbstract_c6ce6628-4e37-42ef-a7dd-219c68891638" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CostsAndExpensesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_620b285c-c288-4516-b9e8-7f356df3c1bf" xlink:to="loc_us-gaap_CostsAndExpensesAbstract_c6ce6628-4e37-42ef-a7dd-219c68891638" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServicesSold_6b734a9c-6037-473f-8b8c-54a8747d6f0d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CostOfGoodsAndServicesSold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_c6ce6628-4e37-42ef-a7dd-219c68891638" xlink:to="loc_us-gaap_CostOfGoodsAndServicesSold_6b734a9c-6037-473f-8b8c-54a8747d6f0d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpense_5ae04f0e-3e14-4486-8e97-0b280066d4e6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ResearchAndDevelopmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_c6ce6628-4e37-42ef-a7dd-219c68891638" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpense_5ae04f0e-3e14-4486-8e97-0b280066d4e6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpense_81d73178-92c0-4c86-b8f7-d204fb919cc3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_GeneralAndAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_c6ce6628-4e37-42ef-a7dd-219c68891638" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpense_81d73178-92c0-4c86-b8f7-d204fb919cc3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCharges_1d6b591e-b7d4-4d85-9131-c2875381d88d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestructuringCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_c6ce6628-4e37-42ef-a7dd-219c68891638" xlink:to="loc_us-gaap_RestructuringCharges_1d6b591e-b7d4-4d85-9131-c2875381d88d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostsAndExpenses_8130992e-0bde-4837-9719-c03c135b0afb" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CostsAndExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_c6ce6628-4e37-42ef-a7dd-219c68891638" xlink:to="loc_us-gaap_CostsAndExpenses_8130992e-0bde-4837-9719-c03c135b0afb" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_aa800cb9-4636-402a-a666-5ba4fb0cd3f4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_620b285c-c288-4516-b9e8-7f356df3c1bf" xlink:to="loc_us-gaap_OperatingIncomeLoss_aa800cb9-4636-402a-a666-5ba4fb0cd3f4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonoperatingIncomeExpenseAbstract_9949a387-dead-47f3-be2e-abb8efe4dac5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NonoperatingIncomeExpenseAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_620b285c-c288-4516-b9e8-7f356df3c1bf" xlink:to="loc_us-gaap_NonoperatingIncomeExpenseAbstract_9949a387-dead-47f3-be2e-abb8efe4dac5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesFairValueAdjustment_b62c6e8f-b8e1-4ca7-8da7-21af271b0926" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LiabilitiesFairValueAdjustment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonoperatingIncomeExpenseAbstract_9949a387-dead-47f3-be2e-abb8efe4dac5" xlink:to="loc_us-gaap_LiabilitiesFairValueAdjustment_b62c6e8f-b8e1-4ca7-8da7-21af271b0926" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_NonCashInterestExpenseRelatedToSaleOfRoyalties_afc62b30-e65f-4dae-a35f-d3372a6eff1e" xlink:href="nktr-20220630.xsd#nktr_NonCashInterestExpenseRelatedToSaleOfRoyalties"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonoperatingIncomeExpenseAbstract_9949a387-dead-47f3-be2e-abb8efe4dac5" xlink:to="loc_nktr_NonCashInterestExpenseRelatedToSaleOfRoyalties_afc62b30-e65f-4dae-a35f-d3372a6eff1e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_3f2405c4-8bbe-4c38-b95a-fd060718c195" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherNonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonoperatingIncomeExpenseAbstract_9949a387-dead-47f3-be2e-abb8efe4dac5" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_3f2405c4-8bbe-4c38-b95a-fd060718c195" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonoperatingIncomeExpense_d647f8d9-d3cb-40ca-bb25-4348955963e4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonoperatingIncomeExpenseAbstract_9949a387-dead-47f3-be2e-abb8efe4dac5" xlink:to="loc_us-gaap_NonoperatingIncomeExpense_d647f8d9-d3cb-40ca-bb25-4348955963e4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_b16d8849-b01c-4306-8529-0535ca288c44" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_620b285c-c288-4516-b9e8-7f356df3c1bf" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_b16d8849-b01c-4306-8529-0535ca288c44" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_80c98453-72a3-4126-abb8-e84d6fb0b8f9" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_620b285c-c288-4516-b9e8-7f356df3c1bf" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_80c98453-72a3-4126-abb8-e84d6fb0b8f9" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_faf6d1d1-33bb-4cc7-a537-0178a639322a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_620b285c-c288-4516-b9e8-7f356df3c1bf" xlink:to="loc_us-gaap_NetIncomeLoss_faf6d1d1-33bb-4cc7-a537-0178a639322a" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasic_e65ba605-0c63-4058-9587-12bd6d244812" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EarningsPerShareBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_620b285c-c288-4516-b9e8-7f356df3c1bf" xlink:to="loc_us-gaap_EarningsPerShareBasic_e65ba605-0c63-4058-9587-12bd6d244812" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareDiluted_e425eb69-5a6b-4726-a880-b5441e686e81" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EarningsPerShareDiluted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_620b285c-c288-4516-b9e8-7f356df3c1bf" xlink:to="loc_us-gaap_EarningsPerShareDiluted_e425eb69-5a6b-4726-a880-b5441e686e81" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_616d8bca-102e-45fc-bb7e-d4ef71a8ac3d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_620b285c-c288-4516-b9e8-7f356df3c1bf" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_616d8bca-102e-45fc-bb7e-d4ef71a8ac3d" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_473c162e-193f-4ee8-b8d7-344b651cd981" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_620b285c-c288-4516-b9e8-7f356df3c1bf" xlink:to="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_473c162e-193f-4ee8-b8d7-344b651cd981" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_e76fd5f8-b397-419a-94c5-0e307f98b3d8" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_620b285c-c288-4516-b9e8-7f356df3c1bf" xlink:to="loc_us-gaap_StatementTable_e76fd5f8-b397-419a-94c5-0e307f98b3d8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_56d40ef7-a512-4051-b34f-80eaca8b5351" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_e76fd5f8-b397-419a-94c5-0e307f98b3d8" xlink:to="loc_srt_ProductOrServiceAxis_56d40ef7-a512-4051-b34f-80eaca8b5351" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_56d40ef7-a512-4051-b34f-80eaca8b5351_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_56d40ef7-a512-4051-b34f-80eaca8b5351" xlink:to="loc_srt_ProductsAndServicesDomain_56d40ef7-a512-4051-b34f-80eaca8b5351_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_ddbdb341-e637-4837-ad65-bef88658d649" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_56d40ef7-a512-4051-b34f-80eaca8b5351" xlink:to="loc_srt_ProductsAndServicesDomain_ddbdb341-e637-4837-ad65-bef88658d649" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductMember_523b6682-3a9c-4465-9abb-5dafb4bd3144" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProductMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_ddbdb341-e637-4837-ad65-bef88658d649" xlink:to="loc_us-gaap_ProductMember_523b6682-3a9c-4465-9abb-5dafb4bd3144" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_NonCashRoyaltyRevenueRelatedToSaleOfFutureRoyaltiesMember_3e5b31cc-98e8-4cee-92e5-21f94c9cb93a" xlink:href="nktr-20220630.xsd#nktr_NonCashRoyaltyRevenueRelatedToSaleOfFutureRoyaltiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_ddbdb341-e637-4837-ad65-bef88658d649" xlink:to="loc_nktr_NonCashRoyaltyRevenueRelatedToSaleOfFutureRoyaltiesMember_3e5b31cc-98e8-4cee-92e5-21f94c9cb93a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_LicenseCollaborationAndOtherRevenueMember_5eba5618-4db3-4549-82ee-e3e0902c264e" xlink:href="nktr-20220630.xsd#nktr_LicenseCollaborationAndOtherRevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_ddbdb341-e637-4837-ad65-bef88658d649" xlink:to="loc_nktr_LicenseCollaborationAndOtherRevenueMember_5eba5618-4db3-4549-82ee-e3e0902c264e" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.nektar.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFSTOCKHOLDERSEQUITY" xlink:type="simple" xlink:href="nktr-20220630.xsd#CONDENSEDCONSOLIDATEDSTATEMENTSOFSTOCKHOLDERSEQUITY"/>
  <link:definitionLink xlink:role="http://www.nektar.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFSTOCKHOLDERSEQUITY" xlink:type="extended" id="idf59daefe9584393bccca94fdf3aaf87_CONDENSEDCONSOLIDATEDSTATEMENTSOFSTOCKHOLDERSEQUITY">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_a79ee8c0-4f1c-41fb-a318-14e5fd693185" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_aac10a1b-fd72-4e36-b390-d8549d3504c6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_a79ee8c0-4f1c-41fb-a318-14e5fd693185" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_aac10a1b-fd72-4e36-b390-d8549d3504c6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesOutstanding_af7e7565-c0fa-4810-bdb4-1576814c3ad5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_aac10a1b-fd72-4e36-b390-d8549d3504c6" xlink:to="loc_us-gaap_SharesOutstanding_af7e7565-c0fa-4810-bdb4-1576814c3ad5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_6826112b-cbb9-4b74-87aa-759d69d31e6c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_aac10a1b-fd72-4e36-b390-d8549d3504c6" xlink:to="loc_us-gaap_StockholdersEquity_6826112b-cbb9-4b74-87aa-759d69d31e6c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation_82d2fe3c-7987-4783-838d-07b8896968cd" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_aac10a1b-fd72-4e36-b390-d8549d3504c6" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation_82d2fe3c-7987-4783-838d-07b8896968cd" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation_9762bfe8-6082-4d53-8b53-2dbeb7e7a5f5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_aac10a1b-fd72-4e36-b390-d8549d3504c6" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation_9762bfe8-6082-4d53-8b53-2dbeb7e7a5f5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_7d1d9a63-39a0-4f7f-83ed-b4ed4623f40d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_aac10a1b-fd72-4e36-b390-d8549d3504c6" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_7d1d9a63-39a0-4f7f-83ed-b4ed4623f40d" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComprehensiveIncomeNetOfTax_9e6204a2-a3a6-4c58-899d-de03117e6fe9" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ComprehensiveIncomeNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_aac10a1b-fd72-4e36-b390-d8549d3504c6" xlink:to="loc_us-gaap_ComprehensiveIncomeNetOfTax_9e6204a2-a3a6-4c58-899d-de03117e6fe9" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesOutstanding_0bd17237-5b00-450e-a153-8f22d43a86c7" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_a099a131-05e6-41d1-bc26-be5263039458" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockholdersEquity"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_feb0bc43-375b-420f-8dae-642a837a6a5b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_a79ee8c0-4f1c-41fb-a318-14e5fd693185" xlink:to="loc_us-gaap_StatementTable_feb0bc43-375b-420f-8dae-642a837a6a5b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_486e3ad3-3a0e-4067-a226-be9fb617ba36" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_feb0bc43-375b-420f-8dae-642a837a6a5b" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_486e3ad3-3a0e-4067-a226-be9fb617ba36" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_486e3ad3-3a0e-4067-a226-be9fb617ba36_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_486e3ad3-3a0e-4067-a226-be9fb617ba36" xlink:to="loc_us-gaap_EquityComponentDomain_486e3ad3-3a0e-4067-a226-be9fb617ba36_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_614040e1-56fb-4f6a-8b41-c65b6b0d40cb" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_486e3ad3-3a0e-4067-a226-be9fb617ba36" xlink:to="loc_us-gaap_EquityComponentDomain_614040e1-56fb-4f6a-8b41-c65b6b0d40cb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_bd3668e6-2fdd-451c-b100-703bbbd582f2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_614040e1-56fb-4f6a-8b41-c65b6b0d40cb" xlink:to="loc_us-gaap_CommonStockMember_bd3668e6-2fdd-451c-b100-703bbbd582f2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_838de474-dd31-484a-9182-16b7190e594e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_614040e1-56fb-4f6a-8b41-c65b6b0d40cb" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_838de474-dd31-484a-9182-16b7190e594e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_9194b0d7-fb97-440c-9885-8805a5e77b6e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_614040e1-56fb-4f6a-8b41-c65b6b0d40cb" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_9194b0d7-fb97-440c-9885-8805a5e77b6e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_34d30b33-6690-4ce8-b2e9-bf714c8f4ecc" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_614040e1-56fb-4f6a-8b41-c65b6b0d40cb" xlink:to="loc_us-gaap_RetainedEarningsMember_34d30b33-6690-4ce8-b2e9-bf714c8f4ecc" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.nektar.com/role/OrganizationandSummaryofSignificantAccountingPoliciesAdditionalInformationDetail" xlink:type="simple" xlink:href="nktr-20220630.xsd#OrganizationandSummaryofSignificantAccountingPoliciesAdditionalInformationDetail"/>
  <link:definitionLink xlink:role="http://www.nektar.com/role/OrganizationandSummaryofSignificantAccountingPoliciesAdditionalInformationDetail" xlink:type="extended" id="i4fea874754244ec78ed2b3d65b8473b0_OrganizationandSummaryofSignificantAccountingPoliciesAdditionalInformationDetail">
    <link:loc xlink:type="locator" xlink:label="loc_nktr_OrganizationAndSummaryOfSignificantAccountingPoliciesLineItems_af55663d-fd8d-450e-9172-c7396f3799da" xlink:href="nktr-20220630.xsd#nktr_OrganizationAndSummaryOfSignificantAccountingPoliciesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_CashRestrictedCashCashEquivalentsAndAvailableForSaleInvestments_6263c496-a5b9-42f4-8330-ffaca2bc67d6" xlink:href="nktr-20220630.xsd#nktr_CashRestrictedCashCashEquivalentsAndAvailableForSaleInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_nktr_OrganizationAndSummaryOfSignificantAccountingPoliciesLineItems_af55663d-fd8d-450e-9172-c7396f3799da" xlink:to="loc_nktr_CashRestrictedCashCashEquivalentsAndAvailableForSaleInvestments_6263c496-a5b9-42f4-8330-ffaca2bc67d6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringAndRelatedCostNumberOfPositionsEliminatedPeriodPercent_e829daf2-5e2c-42b7-88ba-231897ebdaa2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestructuringAndRelatedCostNumberOfPositionsEliminatedPeriodPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_nktr_OrganizationAndSummaryOfSignificantAccountingPoliciesLineItems_af55663d-fd8d-450e-9172-c7396f3799da" xlink:to="loc_us-gaap_RestructuringAndRelatedCostNumberOfPositionsEliminatedPeriodPercent_e829daf2-5e2c-42b7-88ba-231897ebdaa2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_18e414b0-0c31-4b0e-84d9-423793aaaad8" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccountsReceivableNetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_nktr_OrganizationAndSummaryOfSignificantAccountingPoliciesLineItems_af55663d-fd8d-450e-9172-c7396f3799da" xlink:to="loc_us-gaap_AccountsReceivableNetCurrent_18e414b0-0c31-4b0e-84d9-423793aaaad8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProvisionForDoubtfulAccounts_ae968bb8-a53d-48a2-9c9b-3f899ff87535" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProvisionForDoubtfulAccounts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_nktr_OrganizationAndSummaryOfSignificantAccountingPoliciesLineItems_af55663d-fd8d-450e-9172-c7396f3799da" xlink:to="loc_us-gaap_ProvisionForDoubtfulAccounts_ae968bb8-a53d-48a2-9c9b-3f899ff87535" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_OrganizationAndSummaryOfSignificantAccountingPoliciesTable_95f1c721-1ad7-4bff-851e-8c24c9b9a1ef" xlink:href="nktr-20220630.xsd#nktr_OrganizationAndSummaryOfSignificantAccountingPoliciesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_nktr_OrganizationAndSummaryOfSignificantAccountingPoliciesLineItems_af55663d-fd8d-450e-9172-c7396f3799da" xlink:to="loc_nktr_OrganizationAndSummaryOfSignificantAccountingPoliciesTable_95f1c721-1ad7-4bff-851e-8c24c9b9a1ef" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_3453bcd6-d847-4dbc-92d1-2db4c5ac63a9" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_nktr_OrganizationAndSummaryOfSignificantAccountingPoliciesTable_95f1c721-1ad7-4bff-851e-8c24c9b9a1ef" xlink:to="loc_srt_CounterpartyNameAxis_3453bcd6-d847-4dbc-92d1-2db4c5ac63a9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_3453bcd6-d847-4dbc-92d1-2db4c5ac63a9_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_3453bcd6-d847-4dbc-92d1-2db4c5ac63a9" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_3453bcd6-d847-4dbc-92d1-2db4c5ac63a9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_f8e25479-cbee-48c4-972e-c58b2f7d86f9" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_3453bcd6-d847-4dbc-92d1-2db4c5ac63a9" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_f8e25479-cbee-48c4-972e-c58b2f7d86f9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_BristolMyersSquibbCollaborationAgreementMember_4b007fc7-3f86-4c73-bd32-23866ce84955" xlink:href="nktr-20220630.xsd#nktr_BristolMyersSquibbCollaborationAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_f8e25479-cbee-48c4-972e-c58b2f7d86f9" xlink:to="loc_nktr_BristolMyersSquibbCollaborationAgreementMember_4b007fc7-3f86-4c73-bd32-23866ce84955" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveAxis_4a86ff36-70bb-4b8f-9d16-c09efcecde94" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestructuringCostAndReserveAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_nktr_OrganizationAndSummaryOfSignificantAccountingPoliciesTable_95f1c721-1ad7-4bff-851e-8c24c9b9a1ef" xlink:to="loc_us-gaap_RestructuringCostAndReserveAxis_4a86ff36-70bb-4b8f-9d16-c09efcecde94" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_4a86ff36-70bb-4b8f-9d16-c09efcecde94_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_4a86ff36-70bb-4b8f-9d16-c09efcecde94" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_4a86ff36-70bb-4b8f-9d16-c09efcecde94_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_5ee943bc-542f-4b11-95fe-eedc6b5a4f33" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_4a86ff36-70bb-4b8f-9d16-c09efcecde94" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_5ee943bc-542f-4b11-95fe-eedc6b5a4f33" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeSeveranceMember_72b7c33e-725d-48bb-bdae-be611c1303e8" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EmployeeSeveranceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_5ee943bc-542f-4b11-95fe-eedc6b5a4f33" xlink:to="loc_us-gaap_EmployeeSeveranceMember_72b7c33e-725d-48bb-bdae-be611c1303e8" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.nektar.com/role/CashandInvestmentsinMarketableSecuritiesAdditionalInformationDetail" xlink:type="simple" xlink:href="nktr-20220630.xsd#CashandInvestmentsinMarketableSecuritiesAdditionalInformationDetail"/>
  <link:definitionLink xlink:role="http://www.nektar.com/role/CashandInvestmentsinMarketableSecuritiesAdditionalInformationDetail" xlink:type="extended" id="ife9f2f3510a04863b3992cc75da17b31_CashandInvestmentsinMarketableSecuritiesAdditionalInformationDetail">
    <link:loc xlink:type="locator" xlink:label="loc_nktr_CashAndInvestmentsInMarketableSecuritiesLineItems_4eb23963-42bb-4576-83a1-b29871191eb1" xlink:href="nktr-20220630.xsd#nktr_CashAndInvestmentsInMarketableSecuritiesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_DebtInvestmentMaximumMaturityPeriod_c4cb8b31-cb56-47a7-bb52-17d81011db93" xlink:href="nktr-20220630.xsd#nktr_DebtInvestmentMaximumMaturityPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_nktr_CashAndInvestmentsInMarketableSecuritiesLineItems_4eb23963-42bb-4576-83a1-b29871191eb1" xlink:to="loc_nktr_DebtInvestmentMaximumMaturityPeriod_c4cb8b31-cb56-47a7-bb52-17d81011db93" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_DebtInvestmentMaturityTerm_c7cb76ad-050c-4d40-ab3f-8a86b4cb9d43" xlink:href="nktr-20220630.xsd#nktr_DebtInvestmentMaturityTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_nktr_CashAndInvestmentsInMarketableSecuritiesLineItems_4eb23963-42bb-4576-83a1-b29871191eb1" xlink:to="loc_nktr_DebtInvestmentMaturityTerm_c7cb76ad-050c-4d40-ab3f-8a86b4cb9d43" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_LongTermInvestmentMaturityPeriod_097ddac3-0786-42c8-a325-f6a0bfde4072" xlink:href="nktr-20220630.xsd#nktr_LongTermInvestmentMaturityPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_nktr_CashAndInvestmentsInMarketableSecuritiesLineItems_4eb23963-42bb-4576-83a1-b29871191eb1" xlink:to="loc_nktr_LongTermInvestmentMaturityPeriod_097ddac3-0786-42c8-a325-f6a0bfde4072" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_ad294611-2be4-43ee-bdc9-dd64cd6dda22" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_nktr_CashAndInvestmentsInMarketableSecuritiesLineItems_4eb23963-42bb-4576-83a1-b29871191eb1" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_ad294611-2be4-43ee-bdc9-dd64cd6dda22" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_CashAndInvestmentsInMarketableSecuritiesTable_70030f2c-38d5-4fa9-af6a-b16bfd7eea28" xlink:href="nktr-20220630.xsd#nktr_CashAndInvestmentsInMarketableSecuritiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_nktr_CashAndInvestmentsInMarketableSecuritiesLineItems_4eb23963-42bb-4576-83a1-b29871191eb1" xlink:to="loc_nktr_CashAndInvestmentsInMarketableSecuritiesTable_70030f2c-38d5-4fa9-af6a-b16bfd7eea28" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_772cfae2-485e-4988-9f20-5838bfabe6a1" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_nktr_CashAndInvestmentsInMarketableSecuritiesTable_70030f2c-38d5-4fa9-af6a-b16bfd7eea28" xlink:to="loc_srt_RangeAxis_772cfae2-485e-4988-9f20-5838bfabe6a1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_772cfae2-485e-4988-9f20-5838bfabe6a1_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_772cfae2-485e-4988-9f20-5838bfabe6a1" xlink:to="loc_srt_RangeMember_772cfae2-485e-4988-9f20-5838bfabe6a1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_9264bcfc-5114-440c-ad36-6982890c170c" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_772cfae2-485e-4988-9f20-5838bfabe6a1" xlink:to="loc_srt_RangeMember_9264bcfc-5114-440c-ad36-6982890c170c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_053684df-9296-4ece-be66-d1bae1cadfb3" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_9264bcfc-5114-440c-ad36-6982890c170c" xlink:to="loc_srt_MinimumMember_053684df-9296-4ece-be66-d1bae1cadfb3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_d6677b83-cd3a-4b97-9756-d4341055913d" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_9264bcfc-5114-440c-ad36-6982890c170c" xlink:to="loc_srt_MaximumMember_d6677b83-cd3a-4b97-9756-d4341055913d" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.nektar.com/role/CashandInvestmentsinMarketableSecuritiesPortfolioofCashandInvestmentsinMarketableSecuritiesDetail" xlink:type="simple" xlink:href="nktr-20220630.xsd#CashandInvestmentsinMarketableSecuritiesPortfolioofCashandInvestmentsinMarketableSecuritiesDetail"/>
  <link:definitionLink xlink:role="http://www.nektar.com/role/CashandInvestmentsinMarketableSecuritiesPortfolioofCashandInvestmentsinMarketableSecuritiesDetail" xlink:type="extended" id="i42fe2650583442358893aedce89f8ba6_CashandInvestmentsinMarketableSecuritiesPortfolioofCashandInvestmentsinMarketableSecuritiesDetail">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_f8cc548e-330b-4e82-a754-272399d71b38" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_e76db2b4-d513-4e76-b975-7a6257312aea" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_f8cc548e-330b-4e82-a754-272399d71b38" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_e76db2b4-d513-4e76-b975-7a6257312aea" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_ab14796a-6ad3-4f6a-a9ae-09cddde8d885" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_f8cc548e-330b-4e82-a754-272399d71b38" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_ab14796a-6ad3-4f6a-a9ae-09cddde8d885" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_8de3a813-8d92-483e-beb9-b2aa6d7ba7e2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_f8cc548e-330b-4e82-a754-272399d71b38" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_8de3a813-8d92-483e-beb9-b2aa6d7ba7e2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_45544daa-4f99-447f-bfde-7fb365b5b769" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_f8cc548e-330b-4e82-a754-272399d71b38" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_45544daa-4f99-447f-bfde-7fb365b5b769" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentsFairValueDisclosure_4fbd56b9-71bc-4176-9f9b-b5712977d28e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvestmentsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_f8cc548e-330b-4e82-a754-272399d71b38" xlink:to="loc_us-gaap_InvestmentsFairValueDisclosure_4fbd56b9-71bc-4176-9f9b-b5712977d28e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Cash_acdb9064-c8ff-4a32-ade8-88bc2b08737b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_Cash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_f8cc548e-330b-4e82-a754-272399d71b38" xlink:to="loc_us-gaap_Cash_acdb9064-c8ff-4a32-ade8-88bc2b08737b" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_CashRestrictedCashCashEquivalentsAndAvailableForSaleInvestments_f8f1944b-6c5b-491c-b136-cdfa2c9d2dc6" xlink:href="nktr-20220630.xsd#nktr_CashRestrictedCashCashEquivalentsAndAvailableForSaleInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_f8cc548e-330b-4e82-a754-272399d71b38" xlink:to="loc_nktr_CashRestrictedCashCashEquivalentsAndAvailableForSaleInvestments_f8f1944b-6c5b-491c-b136-cdfa2c9d2dc6" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_7735d5d5-7072-4516-904d-bac8cea4ad6c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_f8cc548e-330b-4e82-a754-272399d71b38" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_7735d5d5-7072-4516-904d-bac8cea4ad6c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_3849f3bc-6603-4453-b342-91f740cc1edf" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_7735d5d5-7072-4516-904d-bac8cea4ad6c" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_3849f3bc-6603-4453-b342-91f740cc1edf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_3849f3bc-6603-4453-b342-91f740cc1edf_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_3849f3bc-6603-4453-b342-91f740cc1edf" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_3849f3bc-6603-4453-b342-91f740cc1edf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_ae971c25-6701-4cb4-80cf-e273ceaae0cd" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_3849f3bc-6603-4453-b342-91f740cc1edf" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_ae971c25-6701-4cb4-80cf-e273ceaae0cd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_7feb2c8e-d5dd-4738-8ac6-4c131d76a878" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_ae971c25-6701-4cb4-80cf-e273ceaae0cd" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_7feb2c8e-d5dd-4738-8ac6-4c131d76a878" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_442b0db5-41e7-4cc8-a620-368ac7172c4c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_ae971c25-6701-4cb4-80cf-e273ceaae0cd" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_442b0db5-41e7-4cc8-a620-368ac7172c4c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_54373af7-eec2-4c00-b058-7639d7450dc5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_7735d5d5-7072-4516-904d-bac8cea4ad6c" xlink:to="loc_us-gaap_FinancialInstrumentAxis_54373af7-eec2-4c00-b058-7639d7450dc5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_54373af7-eec2-4c00-b058-7639d7450dc5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_54373af7-eec2-4c00-b058-7639d7450dc5" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_54373af7-eec2-4c00-b058-7639d7450dc5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_f617f26e-4562-4d0a-8500-d6af3e6fee3e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_54373af7-eec2-4c00-b058-7639d7450dc5" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_f617f26e-4562-4d0a-8500-d6af3e6fee3e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateDebtSecuritiesMember_60b1405b-cf00-43a7-a544-6aa2f9932cc0" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CorporateDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_f617f26e-4562-4d0a-8500-d6af3e6fee3e" xlink:to="loc_us-gaap_CorporateDebtSecuritiesMember_60b1405b-cf00-43a7-a544-6aa2f9932cc0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialPaperMember_47b1047a-4d14-448e-a5b7-3718f35ec67f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommercialPaperMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_f617f26e-4562-4d0a-8500-d6af3e6fee3e" xlink:to="loc_us-gaap_CommercialPaperMember_47b1047a-4d14-448e-a5b7-3718f35ec67f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_79559767-dbf1-4146-9433-d06837f90bfa" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_USGovernmentAgenciesDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_f617f26e-4562-4d0a-8500-d6af3e6fee3e" xlink:to="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_79559767-dbf1-4146-9433-d06837f90bfa" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MoneyMarketFundsMember_95522f26-deef-409b-933f-6e5b28ec85c5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_MoneyMarketFundsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_f617f26e-4562-4d0a-8500-d6af3e6fee3e" xlink:to="loc_us-gaap_MoneyMarketFundsMember_95522f26-deef-409b-933f-6e5b28ec85c5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CertificatesOfDepositMember_60b1a3e9-d329-4c02-bf19-d8e9bd291081" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CertificatesOfDepositMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_f617f26e-4562-4d0a-8500-d6af3e6fee3e" xlink:to="loc_us-gaap_CertificatesOfDepositMember_60b1a3e9-d329-4c02-bf19-d8e9bd291081" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.nektar.com/role/CoDevelopmentAgreementwithSFJPharmaceuticalsandDevelopmentDerivativeLiabilityAdditionalInformationDetails" xlink:type="simple" xlink:href="nktr-20220630.xsd#CoDevelopmentAgreementwithSFJPharmaceuticalsandDevelopmentDerivativeLiabilityAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://www.nektar.com/role/CoDevelopmentAgreementwithSFJPharmaceuticalsandDevelopmentDerivativeLiabilityAdditionalInformationDetails" xlink:type="extended" id="iccfd315c7013468fb34c7a035e9c4b26_CoDevelopmentAgreementwithSFJPharmaceuticalsandDevelopmentDerivativeLiabilityAdditionalInformationDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_4c209c2a-ef9f-4d95-8814-06680bbdda72" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_CollaborativeArrangementCommittedFunding_018c867e-ef8e-49a4-9146-7bbad070e5cd" xlink:href="nktr-20220630.xsd#nktr_CollaborativeArrangementCommittedFunding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_4c209c2a-ef9f-4d95-8814-06680bbdda72" xlink:to="loc_nktr_CollaborativeArrangementCommittedFunding_018c867e-ef8e-49a4-9146-7bbad070e5cd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_CollaborativeArrangementSuccessBasedPaymentsAmount_640769ba-6efc-46d6-baf0-3dd493a13cb6" xlink:href="nktr-20220630.xsd#nktr_CollaborativeArrangementSuccessBasedPaymentsAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_4c209c2a-ef9f-4d95-8814-06680bbdda72" xlink:to="loc_nktr_CollaborativeArrangementSuccessBasedPaymentsAmount_640769ba-6efc-46d6-baf0-3dd493a13cb6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilities_b4b1120f-948e-4976-bd33-8316b4388721" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_4c209c2a-ef9f-4d95-8814-06680bbdda72" xlink:to="loc_us-gaap_DerivativeLiabilities_b4b1120f-948e-4976-bd33-8316b4388721" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_2f891cfc-e6df-4b21-a7bb-5ce25b907f59" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_4c209c2a-ef9f-4d95-8814-06680bbdda72" xlink:to="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_2f891cfc-e6df-4b21-a7bb-5ce25b907f59" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_678e3520-e47f-4b6a-8bc4-36feb303193a" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_2f891cfc-e6df-4b21-a7bb-5ce25b907f59" xlink:to="loc_srt_CounterpartyNameAxis_678e3520-e47f-4b6a-8bc4-36feb303193a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_678e3520-e47f-4b6a-8bc4-36feb303193a_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_678e3520-e47f-4b6a-8bc4-36feb303193a" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_678e3520-e47f-4b6a-8bc4-36feb303193a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_74a53083-9af1-417e-8704-3dabe4d7dbb5" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_678e3520-e47f-4b6a-8bc4-36feb303193a" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_74a53083-9af1-417e-8704-3dabe4d7dbb5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_SFJPharmaceuticalsMember_99e643bf-0321-4dad-b846-ea81f5989746" xlink:href="nktr-20220630.xsd#nktr_SFJPharmaceuticalsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_74a53083-9af1-417e-8704-3dabe4d7dbb5" xlink:to="loc_nktr_SFJPharmaceuticalsMember_99e643bf-0321-4dad-b846-ea81f5989746" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.nektar.com/role/CoDevelopmentAgreementwithSFJPharmaceuticalsandDevelopmentDerivativeLiabilityFairValueofDerivativeLiabilityDetails" xlink:type="simple" xlink:href="nktr-20220630.xsd#CoDevelopmentAgreementwithSFJPharmaceuticalsandDevelopmentDerivativeLiabilityFairValueofDerivativeLiabilityDetails"/>
  <link:definitionLink xlink:role="http://www.nektar.com/role/CoDevelopmentAgreementwithSFJPharmaceuticalsandDevelopmentDerivativeLiabilityFairValueofDerivativeLiabilityDetails" xlink:type="extended" id="i55606ef0a5e842e8a5cb1552e1b2c307_CoDevelopmentAgreementwithSFJPharmaceuticalsandDevelopmentDerivativeLiabilityFairValueofDerivativeLiabilityDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_89502ce9-4db7-4219-a78d-b2c8e84522e1" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_1a95c97f-7c12-44f5-9568-f9282cf71efa" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_89502ce9-4db7-4219-a78d-b2c8e84522e1" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_1a95c97f-7c12-44f5-9568-f9282cf71efa" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_7ac406d0-6dbe-4cab-90fc-131a413d4864" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_1a95c97f-7c12-44f5-9568-f9282cf71efa" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_7ac406d0-6dbe-4cab-90fc-131a413d4864" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityResearchAndDevelopmentExpense_e14deccf-233c-4dc6-9d61-d5045c48e40d" xlink:href="nktr-20220630.xsd#nktr_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityResearchAndDevelopmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_1a95c97f-7c12-44f5-9568-f9282cf71efa" xlink:to="loc_nktr_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityResearchAndDevelopmentExpense_e14deccf-233c-4dc6-9d61-d5045c48e40d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityIssues_98cacef1-cd92-47b0-abf0-f95d500c2411" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_1a95c97f-7c12-44f5-9568-f9282cf71efa" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityIssues_98cacef1-cd92-47b0-abf0-f95d500c2411" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInOtherComprehensiveIncome_9f0e1668-883f-4245-97d3-d0465ca69e66" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInOtherComprehensiveIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_1a95c97f-7c12-44f5-9568-f9282cf71efa" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInOtherComprehensiveIncome_9f0e1668-883f-4245-97d3-d0465ca69e66" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_ea77e740-6514-492c-9d71-3bf2bd3d46eb" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_9ca7c530-d56c-4354-ad02-de82b9a99119" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_89502ce9-4db7-4219-a78d-b2c8e84522e1" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_9ca7c530-d56c-4354-ad02-de82b9a99119" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByLiabilityClassAxis_dbad52fe-5af8-43ea-ac21-7c79930078ba" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByLiabilityClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_9ca7c530-d56c-4354-ad02-de82b9a99119" xlink:to="loc_us-gaap_FairValueByLiabilityClassAxis_dbad52fe-5af8-43ea-ac21-7c79930078ba" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_dbad52fe-5af8-43ea-ac21-7c79930078ba_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByLiabilityClassAxis_dbad52fe-5af8-43ea-ac21-7c79930078ba" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_dbad52fe-5af8-43ea-ac21-7c79930078ba_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_de885275-5d39-42d6-bbaf-8462053f3544" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByLiabilityClassAxis_dbad52fe-5af8-43ea-ac21-7c79930078ba" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_de885275-5d39-42d6-bbaf-8462053f3544" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeFinancialInstrumentsLiabilitiesMember_ddb70e75-d665-4e5e-9585-c759af9a112d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeFinancialInstrumentsLiabilitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_de885275-5d39-42d6-bbaf-8462053f3544" xlink:to="loc_us-gaap_DerivativeFinancialInstrumentsLiabilitiesMember_ddb70e75-d665-4e5e-9585-c759af9a112d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_7a520373-ff77-4942-b209-5239eaa51e17" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_9ca7c530-d56c-4354-ad02-de82b9a99119" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_7a520373-ff77-4942-b209-5239eaa51e17" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_7a520373-ff77-4942-b209-5239eaa51e17_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_7a520373-ff77-4942-b209-5239eaa51e17" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_7a520373-ff77-4942-b209-5239eaa51e17_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_a5124967-83bf-4e6a-84cb-f9695c987950" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_7a520373-ff77-4942-b209-5239eaa51e17" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_a5124967-83bf-4e6a-84cb-f9695c987950" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_bcdb6918-e857-4803-89a3-454d45f3f63d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_a5124967-83bf-4e6a-84cb-f9695c987950" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_bcdb6918-e857-4803-89a3-454d45f3f63d" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.nektar.com/role/LiabilitiesRelatedtoSalesofFutureRoyaltiesActivityWithintheLiabilityAccountDetails" xlink:type="simple" xlink:href="nktr-20220630.xsd#LiabilitiesRelatedtoSalesofFutureRoyaltiesActivityWithintheLiabilityAccountDetails"/>
  <link:definitionLink xlink:role="http://www.nektar.com/role/LiabilitiesRelatedtoSalesofFutureRoyaltiesActivityWithintheLiabilityAccountDetails" xlink:type="extended" id="i9aa6cc72cd2a45bba2c8b1c048ec3ce5_LiabilitiesRelatedtoSalesofFutureRoyaltiesActivityWithintheLiabilityAccountDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_1c14576f-76b8-4a0a-bc73-60a544bde491" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_RoyaltyMonetizationProceeds_bba4c9d4-db19-4b3a-a9a1-230974ce7734" xlink:href="nktr-20220630.xsd#nktr_RoyaltyMonetizationProceeds"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_1c14576f-76b8-4a0a-bc73-60a544bde491" xlink:to="loc_nktr_RoyaltyMonetizationProceeds_bba4c9d4-db19-4b3a-a9a1-230974ce7734" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_NonCashRoyaltyRevenueRelatedToSaleOfFutureRoyalties_9974e4c4-87c7-4b25-a921-e2ef7a7e7c3f" xlink:href="nktr-20220630.xsd#nktr_NonCashRoyaltyRevenueRelatedToSaleOfFutureRoyalties"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_1c14576f-76b8-4a0a-bc73-60a544bde491" xlink:to="loc_nktr_NonCashRoyaltyRevenueRelatedToSaleOfFutureRoyalties_9974e4c4-87c7-4b25-a921-e2ef7a7e7c3f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_NonCashInterestExpenseRelatedToSaleOfRoyalties_92ba6e94-de7e-4cd5-a9b0-68f59943057f" xlink:href="nktr-20220630.xsd#nktr_NonCashInterestExpenseRelatedToSaleOfRoyalties"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_1c14576f-76b8-4a0a-bc73-60a544bde491" xlink:to="loc_nktr_NonCashInterestExpenseRelatedToSaleOfRoyalties_92ba6e94-de7e-4cd5-a9b0-68f59943057f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_PartialRepaymentOfRoyaltySaleProceeds_3dce98ad-2629-4377-a3b1-5e6fefe0118f" xlink:href="nktr-20220630.xsd#nktr_PartialRepaymentOfRoyaltySaleProceeds"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_1c14576f-76b8-4a0a-bc73-60a544bde491" xlink:to="loc_nktr_PartialRepaymentOfRoyaltySaleProceeds_3dce98ad-2629-4377-a3b1-5e6fefe0118f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_GainLossOnRevaluationOfLiabilitiesRelatedToTheSaleOfFutureRoyaltiesGross_7a6035a8-468d-4257-8440-f94045cfca1f" xlink:href="nktr-20220630.xsd#nktr_GainLossOnRevaluationOfLiabilitiesRelatedToTheSaleOfFutureRoyaltiesGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_1c14576f-76b8-4a0a-bc73-60a544bde491" xlink:to="loc_nktr_GainLossOnRevaluationOfLiabilitiesRelatedToTheSaleOfFutureRoyaltiesGross_7a6035a8-468d-4257-8440-f94045cfca1f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_LiabilityRelatedToSaleOfPotentialFutureRoyaltiesNonCurrent_e1087df8-9a63-4b75-a821-57938a9d3f87" xlink:href="nktr-20220630.xsd#nktr_LiabilityRelatedToSaleOfPotentialFutureRoyaltiesNonCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_1c14576f-76b8-4a0a-bc73-60a544bde491" xlink:to="loc_nktr_LiabilityRelatedToSaleOfPotentialFutureRoyaltiesNonCurrent_e1087df8-9a63-4b75-a821-57938a9d3f87" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_LiabilitiesOnSaleOfFutureRoyaltiesUnamortizedTransactionCosts_febf9c86-3bc3-4421-8ca0-e89b26cf4863" xlink:href="nktr-20220630.xsd#nktr_LiabilitiesOnSaleOfFutureRoyaltiesUnamortizedTransactionCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_1c14576f-76b8-4a0a-bc73-60a544bde491" xlink:to="loc_nktr_LiabilitiesOnSaleOfFutureRoyaltiesUnamortizedTransactionCosts_febf9c86-3bc3-4421-8ca0-e89b26cf4863" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_LiabilityRelatedToSaleOfPotentialFutureRoyaltiesNonCurrentNetOfIssuanceCosts_997b49ac-995a-41eb-91dc-b89da5a34667" xlink:href="nktr-20220630.xsd#nktr_LiabilityRelatedToSaleOfPotentialFutureRoyaltiesNonCurrentNetOfIssuanceCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_1c14576f-76b8-4a0a-bc73-60a544bde491" xlink:to="loc_nktr_LiabilityRelatedToSaleOfPotentialFutureRoyaltiesNonCurrentNetOfIssuanceCosts_997b49ac-995a-41eb-91dc-b89da5a34667" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_c3f7d271-2f16-4629-8625-2af79cf37934" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_1c14576f-76b8-4a0a-bc73-60a544bde491" xlink:to="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_c3f7d271-2f16-4629-8625-2af79cf37934" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfArrangementAxis_bedf5d48-e0d5-45be-af3f-ffa0e7935beb" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TypeOfArrangementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_c3f7d271-2f16-4629-8625-2af79cf37934" xlink:to="loc_us-gaap_TypeOfArrangementAxis_bedf5d48-e0d5-45be-af3f-ffa0e7935beb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_bedf5d48-e0d5-45be-af3f-ffa0e7935beb_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TypeOfArrangementAxis_bedf5d48-e0d5-45be-af3f-ffa0e7935beb" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_bedf5d48-e0d5-45be-af3f-ffa0e7935beb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_7c64ec47-c9a1-4dd7-ac43-447c5bf269ed" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TypeOfArrangementAxis_bedf5d48-e0d5-45be-af3f-ffa0e7935beb" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_7c64ec47-c9a1-4dd7-ac43-447c5bf269ed" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_PurchaseAndSaleAgreement2012Member_66ce3307-78f3-4839-9aef-4682590232c3" xlink:href="nktr-20220630.xsd#nktr_PurchaseAndSaleAgreement2012Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_7c64ec47-c9a1-4dd7-ac43-447c5bf269ed" xlink:to="loc_nktr_PurchaseAndSaleAgreement2012Member_66ce3307-78f3-4839-9aef-4682590232c3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_PurchaseAndSaleAgreement2020Member_e9f451ba-79a9-4189-a401-89cdfc5b38fc" xlink:href="nktr-20220630.xsd#nktr_PurchaseAndSaleAgreement2020Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_7c64ec47-c9a1-4dd7-ac43-447c5bf269ed" xlink:to="loc_nktr_PurchaseAndSaleAgreement2020Member_e9f451ba-79a9-4189-a401-89cdfc5b38fc" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.nektar.com/role/LiabilitiesRelatedtoSalesofFutureRoyaltiesAdditionalInformationDetails" xlink:type="simple" xlink:href="nktr-20220630.xsd#LiabilitiesRelatedtoSalesofFutureRoyaltiesAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://www.nektar.com/role/LiabilitiesRelatedtoSalesofFutureRoyaltiesAdditionalInformationDetails" xlink:type="extended" id="i3080f9e0f45a40ca9cbe664c48255c6e_LiabilitiesRelatedtoSalesofFutureRoyaltiesAdditionalInformationDetails">
    <link:loc xlink:type="locator" xlink:label="loc_nktr_LiabilityRelatedToSaleOfFutureRoyaltiesLineItems_9c9fc2d8-fcf4-4fe5-a0c5-f74af6426f95" xlink:href="nktr-20220630.xsd#nktr_LiabilityRelatedToSaleOfFutureRoyaltiesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_RoyaltiesLiabilityMeasurementInput_df761151-26ce-45a0-a421-65d3c99a33ce" xlink:href="nktr-20220630.xsd#nktr_RoyaltiesLiabilityMeasurementInput"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_nktr_LiabilityRelatedToSaleOfFutureRoyaltiesLineItems_9c9fc2d8-fcf4-4fe5-a0c5-f74af6426f95" xlink:to="loc_nktr_RoyaltiesLiabilityMeasurementInput_df761151-26ce-45a0-a421-65d3c99a33ce" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_LiabilityRelatedToSaleOfFutureRoyaltiesTable_592efd78-a18f-4ebd-923d-f97bdf5483ee" xlink:href="nktr-20220630.xsd#nktr_LiabilityRelatedToSaleOfFutureRoyaltiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_nktr_LiabilityRelatedToSaleOfFutureRoyaltiesLineItems_9c9fc2d8-fcf4-4fe5-a0c5-f74af6426f95" xlink:to="loc_nktr_LiabilityRelatedToSaleOfFutureRoyaltiesTable_592efd78-a18f-4ebd-923d-f97bdf5483ee" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfArrangementAxis_cbcf4918-c94d-41c8-97f7-ae0f8f71507b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TypeOfArrangementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_nktr_LiabilityRelatedToSaleOfFutureRoyaltiesTable_592efd78-a18f-4ebd-923d-f97bdf5483ee" xlink:to="loc_us-gaap_TypeOfArrangementAxis_cbcf4918-c94d-41c8-97f7-ae0f8f71507b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_cbcf4918-c94d-41c8-97f7-ae0f8f71507b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TypeOfArrangementAxis_cbcf4918-c94d-41c8-97f7-ae0f8f71507b" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_cbcf4918-c94d-41c8-97f7-ae0f8f71507b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_34376f0c-541d-4cc9-b129-312d1c45fa62" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TypeOfArrangementAxis_cbcf4918-c94d-41c8-97f7-ae0f8f71507b" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_34376f0c-541d-4cc9-b129-312d1c45fa62" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_PurchaseAndSaleAgreement2012Member_80bc7bac-0543-4525-b212-818da46981c4" xlink:href="nktr-20220630.xsd#nktr_PurchaseAndSaleAgreement2012Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_34376f0c-541d-4cc9-b129-312d1c45fa62" xlink:to="loc_nktr_PurchaseAndSaleAgreement2012Member_80bc7bac-0543-4525-b212-818da46981c4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_PurchaseAndSaleAgreement2020Member_5e817b7c-7ec7-4401-a50d-0c539377ba79" xlink:href="nktr-20220630.xsd#nktr_PurchaseAndSaleAgreement2020Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_34376f0c-541d-4cc9-b129-312d1c45fa62" xlink:to="loc_nktr_PurchaseAndSaleAgreement2020Member_5e817b7c-7ec7-4401-a50d-0c539377ba79" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.nektar.com/role/CommitmentsandContingenciesAdditionalInformationDetail" xlink:type="simple" xlink:href="nktr-20220630.xsd#CommitmentsandContingenciesAdditionalInformationDetail"/>
  <link:definitionLink xlink:role="http://www.nektar.com/role/CommitmentsandContingenciesAdditionalInformationDetail" xlink:type="extended" id="ib23ce032b59f4763b28e9cd19b16e66c_CommitmentsandContingenciesAdditionalInformationDetail">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesLineItems_f72ec3b8-4970-42b2-9c8b-aa8a129fdc81" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LossContingenciesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyAccrualAtCarryingValue_16a97e6b-74a1-4455-a5df-7fb5d60c1460" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LossContingencyAccrualAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_f72ec3b8-4970-42b2-9c8b-aa8a129fdc81" xlink:to="loc_us-gaap_LossContingencyAccrualAtCarryingValue_16a97e6b-74a1-4455-a5df-7fb5d60c1460" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesTable_bd9745b0-54c2-4862-8e7b-d513f9d45937" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LossContingenciesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LossContingenciesLineItems_f72ec3b8-4970-42b2-9c8b-aa8a129fdc81" xlink:to="loc_us-gaap_LossContingenciesTable_bd9745b0-54c2-4862-8e7b-d513f9d45937" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_fd5d1f83-5335-4818-ab8c-1c504737ed91" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LossContingenciesByNatureOfContingencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_bd9745b0-54c2-4862-8e7b-d513f9d45937" xlink:to="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_fd5d1f83-5335-4818-ab8c-1c504737ed91" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyNatureDomain_fd5d1f83-5335-4818-ab8c-1c504737ed91_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LossContingencyNatureDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_fd5d1f83-5335-4818-ab8c-1c504737ed91" xlink:to="loc_us-gaap_LossContingencyNatureDomain_fd5d1f83-5335-4818-ab8c-1c504737ed91_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyNatureDomain_da507e21-e006-4bb2-9a0b-b9b305e335fd" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LossContingencyNatureDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_fd5d1f83-5335-4818-ab8c-1c504737ed91" xlink:to="loc_us-gaap_LossContingencyNatureDomain_da507e21-e006-4bb2-9a0b-b9b305e335fd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_LegalMattersMember_fe8ed419-7d82-4655-8c4e-50e1e06eede9" xlink:href="nktr-20220630.xsd#nktr_LegalMattersMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingencyNatureDomain_da507e21-e006-4bb2-9a0b-b9b305e335fd" xlink:to="loc_nktr_LegalMattersMember_fe8ed419-7d82-4655-8c4e-50e1e06eede9" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.nektar.com/role/LicenseandCollaborationAgreementsAdditionalInformationDetails" xlink:type="simple" xlink:href="nktr-20220630.xsd#LicenseandCollaborationAgreementsAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://www.nektar.com/role/LicenseandCollaborationAgreementsAdditionalInformationDetails" xlink:type="extended" id="i6e44b93582e349c2899f88b11e18dae5_LicenseandCollaborationAgreementsAdditionalInformationDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_9bd60b0b-5aab-4dfd-b9cf-43da0de87512" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_PercentageOfSharingInDevelopmentCosts_f8d26dd9-f55e-4c03-9ce1-77b37c928539" xlink:href="nktr-20220630.xsd#nktr_PercentageOfSharingInDevelopmentCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_9bd60b0b-5aab-4dfd-b9cf-43da0de87512" xlink:to="loc_nktr_PercentageOfSharingInDevelopmentCosts_f8d26dd9-f55e-4c03-9ce1-77b37c928539" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_PercentageOfSharingInProductionCosts_74e2f451-331c-46c2-981d-769259936fe7" xlink:href="nktr-20220630.xsd#nktr_PercentageOfSharingInProductionCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_9bd60b0b-5aab-4dfd-b9cf-43da0de87512" xlink:to="loc_nktr_PercentageOfSharingInProductionCosts_74e2f451-331c-46c2-981d-769259936fe7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_UpfrontAndMilestonePaymentsReceivedFromLicenseAgreements_00f60037-689e-421c-824d-0288884fce65" xlink:href="nktr-20220630.xsd#nktr_UpfrontAndMilestonePaymentsReceivedFromLicenseAgreements"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_9bd60b0b-5aab-4dfd-b9cf-43da0de87512" xlink:to="loc_nktr_UpfrontAndMilestonePaymentsReceivedFromLicenseAgreements_00f60037-689e-421c-824d-0288884fce65" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesIssued_0978c691-83d8-4712-9879-6fd0c9b81d9e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_9bd60b0b-5aab-4dfd-b9cf-43da0de87512" xlink:to="loc_us-gaap_SharesIssued_0978c691-83d8-4712-9879-6fd0c9b81d9e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_SaleOfStockConsiderationReceived_afd4e123-52bf-4f5f-b53b-9da3b97ca8b2" xlink:href="nktr-20220630.xsd#nktr_SaleOfStockConsiderationReceived"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_9bd60b0b-5aab-4dfd-b9cf-43da0de87512" xlink:to="loc_nktr_SaleOfStockConsiderationReceived_afd4e123-52bf-4f5f-b53b-9da3b97ca8b2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_PotentialDevelopmentMilestones_22c61f79-128b-4d8f-b035-7f1780cc9f98" xlink:href="nktr-20220630.xsd#nktr_PotentialDevelopmentMilestones"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_9bd60b0b-5aab-4dfd-b9cf-43da0de87512" xlink:to="loc_nktr_PotentialDevelopmentMilestones_22c61f79-128b-4d8f-b035-7f1780cc9f98" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_ReimbursementOfExpenses_183726af-74db-48dd-ac02-c3dacbf56279" xlink:href="nktr-20220630.xsd#nktr_ReimbursementOfExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_9bd60b0b-5aab-4dfd-b9cf-43da0de87512" xlink:to="loc_nktr_ReimbursementOfExpenses_183726af-74db-48dd-ac02-c3dacbf56279" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_7515a399-c8ce-472d-8e6c-a2e24ba5f120" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccountsReceivableNetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_9bd60b0b-5aab-4dfd-b9cf-43da0de87512" xlink:to="loc_us-gaap_AccountsReceivableNetCurrent_7515a399-c8ce-472d-8e6c-a2e24ba5f120" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_UpfrontAndMilestonePaymentsReceivedUnderLicenseAgreement_50884c80-b098-4410-81f8-3a85deb6c988" xlink:href="nktr-20220630.xsd#nktr_UpfrontAndMilestonePaymentsReceivedUnderLicenseAgreement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_9bd60b0b-5aab-4dfd-b9cf-43da0de87512" xlink:to="loc_nktr_UpfrontAndMilestonePaymentsReceivedUnderLicenseAgreement_50884c80-b098-4410-81f8-3a85deb6c988" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_PotentialDevelopmentAndRegulatoryMilestones_741a9a95-6906-4132-8f25-a3b2a3c9757d" xlink:href="nktr-20220630.xsd#nktr_PotentialDevelopmentAndRegulatoryMilestones"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_9bd60b0b-5aab-4dfd-b9cf-43da0de87512" xlink:to="loc_nktr_PotentialDevelopmentAndRegulatoryMilestones_741a9a95-6906-4132-8f25-a3b2a3c9757d" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_PercentageOfSharingInPhaseTwoDevelopmentCosts_620dcf9d-e3ec-4fe2-ae89-7d153af31e4c" xlink:href="nktr-20220630.xsd#nktr_PercentageOfSharingInPhaseTwoDevelopmentCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_9bd60b0b-5aab-4dfd-b9cf-43da0de87512" xlink:to="loc_nktr_PercentageOfSharingInPhaseTwoDevelopmentCosts_620dcf9d-e3ec-4fe2-ae89-7d153af31e4c" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_PercentageOfFundingPhaseThreeDevelopmentCostsOnAnIndicationByIndicationBasisBorne_871e90b0-d881-4cd8-85eb-2bb21cb9043a" xlink:href="nktr-20220630.xsd#nktr_PercentageOfFundingPhaseThreeDevelopmentCostsOnAnIndicationByIndicationBasisBorne"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_9bd60b0b-5aab-4dfd-b9cf-43da0de87512" xlink:to="loc_nktr_PercentageOfFundingPhaseThreeDevelopmentCostsOnAnIndicationByIndicationBasisBorne_871e90b0-d881-4cd8-85eb-2bb21cb9043a" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_PercentageOfDevelopmentMilestonesPaymentsToBeReceivedUnderCertainConditions_9a8d6d33-66e6-4fda-9866-2d306d532a52" xlink:href="nktr-20220630.xsd#nktr_PercentageOfDevelopmentMilestonesPaymentsToBeReceivedUnderCertainConditions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_9bd60b0b-5aab-4dfd-b9cf-43da0de87512" xlink:to="loc_nktr_PercentageOfDevelopmentMilestonesPaymentsToBeReceivedUnderCertainConditions_9a8d6d33-66e6-4fda-9866-2d306d532a52" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_PercentageOfDevelopmentMilestonesPaymentsToBeReceivedIfConditionsOccur_f4d99279-aebd-47da-a895-18eab452ce09" xlink:href="nktr-20220630.xsd#nktr_PercentageOfDevelopmentMilestonesPaymentsToBeReceivedIfConditionsOccur"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_9bd60b0b-5aab-4dfd-b9cf-43da0de87512" xlink:to="loc_nktr_PercentageOfDevelopmentMilestonesPaymentsToBeReceivedIfConditionsOccur_f4d99279-aebd-47da-a895-18eab452ce09" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_7560b1d7-17dd-4310-910d-396ff00cceb4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_9bd60b0b-5aab-4dfd-b9cf-43da0de87512" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_7560b1d7-17dd-4310-910d-396ff00cceb4" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_b3d6cb78-60a0-4908-b33e-393860cea776" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_9bd60b0b-5aab-4dfd-b9cf-43da0de87512" xlink:to="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_b3d6cb78-60a0-4908-b33e-393860cea776" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_7e407f0c-aa13-43df-a2ea-c52eb56c3e01" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_b3d6cb78-60a0-4908-b33e-393860cea776" xlink:to="loc_srt_ProductOrServiceAxis_7e407f0c-aa13-43df-a2ea-c52eb56c3e01" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_7e407f0c-aa13-43df-a2ea-c52eb56c3e01_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_7e407f0c-aa13-43df-a2ea-c52eb56c3e01" xlink:to="loc_srt_ProductsAndServicesDomain_7e407f0c-aa13-43df-a2ea-c52eb56c3e01_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_24ab9a4d-5b77-4378-9be0-667fd871fc96" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_7e407f0c-aa13-43df-a2ea-c52eb56c3e01" xlink:to="loc_srt_ProductsAndServicesDomain_24ab9a4d-5b77-4378-9be0-667fd871fc96" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_Nektar214Member_ee42bb25-48f9-446d-85d4-15b530e52745" xlink:href="nktr-20220630.xsd#nktr_Nektar214Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_24ab9a4d-5b77-4378-9be0-667fd871fc96" xlink:to="loc_nktr_Nektar214Member_ee42bb25-48f9-446d-85d4-15b530e52745" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_NonCashRoyaltyRevenueRelatedToSaleOfFutureRoyaltiesMember_e44ffe28-eb94-4ab2-bed0-921f7de4b27d" xlink:href="nktr-20220630.xsd#nktr_NonCashRoyaltyRevenueRelatedToSaleOfFutureRoyaltiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_24ab9a4d-5b77-4378-9be0-667fd871fc96" xlink:to="loc_nktr_NonCashRoyaltyRevenueRelatedToSaleOfFutureRoyaltiesMember_e44ffe28-eb94-4ab2-bed0-921f7de4b27d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis_1f1b5d41-9931-463c-854d-b323fcc0c52b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_b3d6cb78-60a0-4908-b33e-393860cea776" xlink:to="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis_1f1b5d41-9931-463c-854d-b323fcc0c52b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain_1f1b5d41-9931-463c-854d-b323fcc0c52b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis_1f1b5d41-9931-463c-854d-b323fcc0c52b" xlink:to="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain_1f1b5d41-9931-463c-854d-b323fcc0c52b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain_05e9f3a8-e4d6-4bf0-952c-2c1cfdb73844" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis_1f1b5d41-9931-463c-854d-b323fcc0c52b" xlink:to="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain_05e9f3a8-e4d6-4bf0-952c-2c1cfdb73844" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_OpdivoMember_d87142b9-52cd-4d92-b1d9-f72c6910d627" xlink:href="nktr-20220630.xsd#nktr_OpdivoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersTypeDomain_05e9f3a8-e4d6-4bf0-952c-2c1cfdb73844" xlink:to="loc_nktr_OpdivoMember_d87142b9-52cd-4d92-b1d9-f72c6910d627" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfArrangementAxis_db15af03-2dd3-4273-9beb-42619e50a2e4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TypeOfArrangementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_b3d6cb78-60a0-4908-b33e-393860cea776" xlink:to="loc_us-gaap_TypeOfArrangementAxis_db15af03-2dd3-4273-9beb-42619e50a2e4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_db15af03-2dd3-4273-9beb-42619e50a2e4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TypeOfArrangementAxis_db15af03-2dd3-4273-9beb-42619e50a2e4" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_db15af03-2dd3-4273-9beb-42619e50a2e4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_28fb701e-273a-46e5-8899-979b218c14f4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TypeOfArrangementAxis_db15af03-2dd3-4273-9beb-42619e50a2e4" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_28fb701e-273a-46e5-8899-979b218c14f4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_BristolMyersSquibbCollaborationAgreementMember_0cde5400-18b9-4728-8bfb-4a458132f9d5" xlink:href="nktr-20220630.xsd#nktr_BristolMyersSquibbCollaborationAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_28fb701e-273a-46e5-8899-979b218c14f4" xlink:to="loc_nktr_BristolMyersSquibbCollaborationAgreementMember_0cde5400-18b9-4728-8bfb-4a458132f9d5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_Nektar358Member_1e61762d-2f61-4964-a7ac-6b3203822b74" xlink:href="nktr-20220630.xsd#nktr_Nektar358Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_28fb701e-273a-46e5-8899-979b218c14f4" xlink:to="loc_nktr_Nektar358Member_1e61762d-2f61-4964-a7ac-6b3203822b74" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_14036947-2ab9-43d5-b403-492c192abbea" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_b3d6cb78-60a0-4908-b33e-393860cea776" xlink:to="loc_dei_LegalEntityAxis_14036947-2ab9-43d5-b403-492c192abbea" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_14036947-2ab9-43d5-b403-492c192abbea_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_14036947-2ab9-43d5-b403-492c192abbea" xlink:to="loc_dei_EntityDomain_14036947-2ab9-43d5-b403-492c192abbea_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_a307bf82-8ddb-42a2-8378-a3a2866974ad" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_14036947-2ab9-43d5-b403-492c192abbea" xlink:to="loc_dei_EntityDomain_a307bf82-8ddb-42a2-8378-a3a2866974ad" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_BristolMyersSquibbCompanyMember_fa467d40-0f6a-4cdd-9102-cd79a6a42017" xlink:href="nktr-20220630.xsd#nktr_BristolMyersSquibbCompanyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_a307bf82-8ddb-42a2-8378-a3a2866974ad" xlink:to="loc_nktr_BristolMyersSquibbCompanyMember_fa467d40-0f6a-4cdd-9102-cd79a6a42017" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_EliLillyAndCompanyMember_0b3a5390-066e-477a-a6e2-4fe31618883b" xlink:href="nktr-20220630.xsd#nktr_EliLillyAndCompanyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_a307bf82-8ddb-42a2-8378-a3a2866974ad" xlink:to="loc_nktr_EliLillyAndCompanyMember_0b3a5390-066e-477a-a6e2-4fe31618883b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_EliLillyMember_8855000d-e44d-457c-bafb-24f5be307e55" xlink:href="nktr-20220630.xsd#nktr_EliLillyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_a307bf82-8ddb-42a2-8378-a3a2866974ad" xlink:to="loc_nktr_EliLillyMember_8855000d-e44d-457c-bafb-24f5be307e55" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_OtherPartnerMember_7c14e6fc-78ee-4b2f-9571-8e9300065fe5" xlink:href="nktr-20220630.xsd#nktr_OtherPartnerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_a307bf82-8ddb-42a2-8378-a3a2866974ad" xlink:to="loc_nktr_OtherPartnerMember_7c14e6fc-78ee-4b2f-9571-8e9300065fe5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_391af8a3-8a9f-40a0-a30d-366d87621111" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_b3d6cb78-60a0-4908-b33e-393860cea776" xlink:to="loc_srt_ConsolidatedEntitiesAxis_391af8a3-8a9f-40a0-a30d-366d87621111" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_391af8a3-8a9f-40a0-a30d-366d87621111_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_391af8a3-8a9f-40a0-a30d-366d87621111" xlink:to="loc_srt_ConsolidatedEntitiesDomain_391af8a3-8a9f-40a0-a30d-366d87621111_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_8d7620c6-fbe2-4f38-969b-8dca42bb5a1b" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_391af8a3-8a9f-40a0-a30d-366d87621111" xlink:to="loc_srt_ConsolidatedEntitiesDomain_8d7620c6-fbe2-4f38-969b-8dca42bb5a1b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ParentCompanyMember_a099308a-8ac7-4596-ad0a-10af5a2adf92" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ParentCompanyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_8d7620c6-fbe2-4f38-969b-8dca42bb5a1b" xlink:to="loc_srt_ParentCompanyMember_a099308a-8ac7-4596-ad0a-10af5a2adf92" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_67910d5e-c461-4e0f-9019-bbe2ddb105b4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_b3d6cb78-60a0-4908-b33e-393860cea776" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_67910d5e-c461-4e0f-9019-bbe2ddb105b4" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_67910d5e-c461-4e0f-9019-bbe2ddb105b4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_67910d5e-c461-4e0f-9019-bbe2ddb105b4" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_67910d5e-c461-4e0f-9019-bbe2ddb105b4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_e1d237bb-8c74-4b99-ad83-a924d1b217d3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_67910d5e-c461-4e0f-9019-bbe2ddb105b4" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_e1d237bb-8c74-4b99-ad83-a924d1b217d3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_SharePurchaseAgreementMember_20b5e969-2d24-4878-afb5-0b92746981f6" xlink:href="nktr-20220630.xsd#nktr_SharePurchaseAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_e1d237bb-8c74-4b99-ad83-a924d1b217d3" xlink:to="loc_nktr_SharePurchaseAgreementMember_20b5e969-2d24-4878-afb5-0b92746981f6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_MilestoneAxis_970a2fd9-01e4-47b5-91c3-03c2959cddd9" xlink:href="nktr-20220630.xsd#nktr_MilestoneAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_b3d6cb78-60a0-4908-b33e-393860cea776" xlink:to="loc_nktr_MilestoneAxis_970a2fd9-01e4-47b5-91c3-03c2959cddd9" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_MilestoneDomain_970a2fd9-01e4-47b5-91c3-03c2959cddd9_default" xlink:href="nktr-20220630.xsd#nktr_MilestoneDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_nktr_MilestoneAxis_970a2fd9-01e4-47b5-91c3-03c2959cddd9" xlink:to="loc_nktr_MilestoneDomain_970a2fd9-01e4-47b5-91c3-03c2959cddd9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_MilestoneDomain_d7061206-dad6-4f93-ac02-b362c69cc0b5" xlink:href="nktr-20220630.xsd#nktr_MilestoneDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_nktr_MilestoneAxis_970a2fd9-01e4-47b5-91c3-03c2959cddd9" xlink:to="loc_nktr_MilestoneDomain_d7061206-dad6-4f93-ac02-b362c69cc0b5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_MilestoneOneMember_4e3774f0-20b1-4b92-acc3-160f0e257a5a" xlink:href="nktr-20220630.xsd#nktr_MilestoneOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_nktr_MilestoneDomain_d7061206-dad6-4f93-ac02-b362c69cc0b5" xlink:to="loc_nktr_MilestoneOneMember_4e3774f0-20b1-4b92-acc3-160f0e257a5a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_af8a1b19-a19f-46d2-86ab-179b8f4f2d3f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_b3d6cb78-60a0-4908-b33e-393860cea776" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_af8a1b19-a19f-46d2-86ab-179b8f4f2d3f" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_af8a1b19-a19f-46d2-86ab-179b8f4f2d3f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_af8a1b19-a19f-46d2-86ab-179b8f4f2d3f" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_af8a1b19-a19f-46d2-86ab-179b8f4f2d3f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_b3a13eb6-6271-4487-be1b-661f6d22a709" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_af8a1b19-a19f-46d2-86ab-179b8f4f2d3f" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_b3a13eb6-6271-4487-be1b-661f6d22a709" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpenseMember_58d4fd57-e275-40c5-9a9d-e17031169a97" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ResearchAndDevelopmentExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_b3a13eb6-6271-4487-be1b-661f6d22a709" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpenseMember_58d4fd57-e275-40c5-9a9d-e17031169a97" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_6d07362b-c15c-47f9-b4bc-43da2fe6782b" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_b3d6cb78-60a0-4908-b33e-393860cea776" xlink:to="loc_srt_CounterpartyNameAxis_6d07362b-c15c-47f9-b4bc-43da2fe6782b" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_6d07362b-c15c-47f9-b4bc-43da2fe6782b_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_6d07362b-c15c-47f9-b4bc-43da2fe6782b" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_6d07362b-c15c-47f9-b4bc-43da2fe6782b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_981dce2b-36af-4943-8e20-0cf7347c52c0" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_6d07362b-c15c-47f9-b4bc-43da2fe6782b" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_981dce2b-36af-4943-8e20-0cf7347c52c0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_BristolMyersSquibbCollaborationAgreementMember_7e2a6597-c26a-40c6-b115-28fca277f812" xlink:href="nktr-20220630.xsd#nktr_BristolMyersSquibbCollaborationAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_981dce2b-36af-4943-8e20-0cf7347c52c0" xlink:to="loc_nktr_BristolMyersSquibbCollaborationAgreementMember_7e2a6597-c26a-40c6-b115-28fca277f812" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_d197f467-6a4b-4f78-987d-5111e644225c" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_b3d6cb78-60a0-4908-b33e-393860cea776" xlink:to="loc_srt_RangeAxis_d197f467-6a4b-4f78-987d-5111e644225c" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_d197f467-6a4b-4f78-987d-5111e644225c_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_d197f467-6a4b-4f78-987d-5111e644225c" xlink:to="loc_srt_RangeMember_d197f467-6a4b-4f78-987d-5111e644225c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_1fbafbf6-d5cd-4d6a-b0e1-f7bb2a9bea9d" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_d197f467-6a4b-4f78-987d-5111e644225c" xlink:to="loc_srt_RangeMember_1fbafbf6-d5cd-4d6a-b0e1-f7bb2a9bea9d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_87d809ce-58da-4b1f-83c2-efa5ba3013b5" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_1fbafbf6-d5cd-4d6a-b0e1-f7bb2a9bea9d" xlink:to="loc_srt_MaximumMember_87d809ce-58da-4b1f-83c2-efa5ba3013b5" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.nektar.com/role/RestructuringImpairmentandOtherCostsofTerminatedProgramNarrativeDetails" xlink:type="simple" xlink:href="nktr-20220630.xsd#RestructuringImpairmentandOtherCostsofTerminatedProgramNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.nektar.com/role/RestructuringImpairmentandOtherCostsofTerminatedProgramNarrativeDetails" xlink:type="extended" id="ic2a94d20d643403c9398ebf85d3ac632_RestructuringImpairmentandOtherCostsofTerminatedProgramNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveLineItems_2b9e23e7-e4ad-4f8a-b908-aa2e03c503b4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestructuringCostAndReserveLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityNumberOfEmployees_93ba0bcd-c48a-479d-90fe-40879c4563d4" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityNumberOfEmployees"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_2b9e23e7-e4ad-4f8a-b908-aa2e03c503b4" xlink:to="loc_dei_EntityNumberOfEmployees_93ba0bcd-c48a-479d-90fe-40879c4563d4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossOnContractTermination_8cbba79d-8794-4d52-a026-31d52125ffbf" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LossOnContractTermination"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_2b9e23e7-e4ad-4f8a-b908-aa2e03c503b4" xlink:to="loc_us-gaap_LossOnContractTermination_8cbba79d-8794-4d52-a026-31d52125ffbf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringAndRelatedCostNumberOfPositionsEliminatedPeriodPercent_44fe3117-3b34-428f-a686-11e2fb21e713" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestructuringAndRelatedCostNumberOfPositionsEliminatedPeriodPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_2b9e23e7-e4ad-4f8a-b908-aa2e03c503b4" xlink:to="loc_us-gaap_RestructuringAndRelatedCostNumberOfPositionsEliminatedPeriodPercent_44fe3117-3b34-428f-a686-11e2fb21e713" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_6a62dec4-29af-413d-bbd8-fd08ba972cd3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfRestructuringAndRelatedCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_2b9e23e7-e4ad-4f8a-b908-aa2e03c503b4" xlink:to="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_6a62dec4-29af-413d-bbd8-fd08ba972cd3" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveAxis_6c86de8d-ace6-4e42-b40b-abeb4942d53b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestructuringCostAndReserveAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_6a62dec4-29af-413d-bbd8-fd08ba972cd3" xlink:to="loc_us-gaap_RestructuringCostAndReserveAxis_6c86de8d-ace6-4e42-b40b-abeb4942d53b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_6c86de8d-ace6-4e42-b40b-abeb4942d53b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_6c86de8d-ace6-4e42-b40b-abeb4942d53b" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_6c86de8d-ace6-4e42-b40b-abeb4942d53b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_17b1e929-c51a-47a0-9919-6ad5adfc042c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_6c86de8d-ace6-4e42-b40b-abeb4942d53b" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_17b1e929-c51a-47a0-9919-6ad5adfc042c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeSeveranceMember_673b82e9-c9b1-4b3f-9a93-11f2c46008f1" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EmployeeSeveranceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_17b1e929-c51a-47a0-9919-6ad5adfc042c" xlink:to="loc_us-gaap_EmployeeSeveranceMember_673b82e9-c9b1-4b3f-9a93-11f2c46008f1" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.nektar.com/role/RestructuringImpairmentandOtherCostsofTerminatedProgramRestructuringReserveRollforwardDetails" xlink:type="simple" xlink:href="nktr-20220630.xsd#RestructuringImpairmentandOtherCostsofTerminatedProgramRestructuringReserveRollforwardDetails"/>
  <link:definitionLink xlink:role="http://www.nektar.com/role/RestructuringImpairmentandOtherCostsofTerminatedProgramRestructuringReserveRollforwardDetails" xlink:type="extended" id="i907afbecd1c64688b172cdadd2e7efdf_RestructuringImpairmentandOtherCostsofTerminatedProgramRestructuringReserveRollforwardDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveLineItems_6919eacb-c1b1-498a-883c-18d74a06f7c3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestructuringCostAndReserveLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringAndRelatedCostExpectedCost1_6c8164c3-f0f2-46c6-9c60-b91f99d78199" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestructuringAndRelatedCostExpectedCost1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_6919eacb-c1b1-498a-883c-18d74a06f7c3" xlink:to="loc_us-gaap_RestructuringAndRelatedCostExpectedCost1_6c8164c3-f0f2-46c6-9c60-b91f99d78199" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserveRollForward_c9494e15-50db-49fc-9a57-b10550029f7c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestructuringReserveRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_6919eacb-c1b1-498a-883c-18d74a06f7c3" xlink:to="loc_us-gaap_RestructuringReserveRollForward_c9494e15-50db-49fc-9a57-b10550029f7c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserve_d44ec4ea-c124-48b7-8d45-b48b7c34cbbf" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestructuringReserve"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringReserveRollForward_c9494e15-50db-49fc-9a57-b10550029f7c" xlink:to="loc_us-gaap_RestructuringReserve_d44ec4ea-c124-48b7-8d45-b48b7c34cbbf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCharges_d3b90934-5c8e-43c2-ad52-e5c08577bf6e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestructuringCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringReserveRollForward_c9494e15-50db-49fc-9a57-b10550029f7c" xlink:to="loc_us-gaap_RestructuringCharges_d3b90934-5c8e-43c2-ad52-e5c08577bf6e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForRestructuring_d24c7c70-cbfb-4da0-ae38-e170a3131cf6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PaymentsForRestructuring"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringReserveRollForward_c9494e15-50db-49fc-9a57-b10550029f7c" xlink:to="loc_us-gaap_PaymentsForRestructuring_d24c7c70-cbfb-4da0-ae38-e170a3131cf6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserve_0ab6e7d4-dc1e-47f4-860d-025d2ceefd67" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestructuringReserve"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_2d0acaee-99ac-4ea2-a5fd-f369ee124298" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfRestructuringAndRelatedCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_6919eacb-c1b1-498a-883c-18d74a06f7c3" xlink:to="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_2d0acaee-99ac-4ea2-a5fd-f369ee124298" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveAxis_26b062b9-5d7f-4154-bffd-423998c6bbc1" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestructuringCostAndReserveAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_2d0acaee-99ac-4ea2-a5fd-f369ee124298" xlink:to="loc_us-gaap_RestructuringCostAndReserveAxis_26b062b9-5d7f-4154-bffd-423998c6bbc1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_26b062b9-5d7f-4154-bffd-423998c6bbc1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_26b062b9-5d7f-4154-bffd-423998c6bbc1" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_26b062b9-5d7f-4154-bffd-423998c6bbc1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_0bc8550f-cc72-42d1-8acb-a18b5970bdc1" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_26b062b9-5d7f-4154-bffd-423998c6bbc1" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_0bc8550f-cc72-42d1-8acb-a18b5970bdc1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeSeveranceMember_e1c9d471-f509-4494-a0fd-d4c225d18e92" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EmployeeSeveranceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_0bc8550f-cc72-42d1-8acb-a18b5970bdc1" xlink:to="loc_us-gaap_EmployeeSeveranceMember_e1c9d471-f509-4494-a0fd-d4c225d18e92" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_EmployeeSeveranceWithNoServicePeriodMember_2bba9c3a-a776-4553-896b-9a209e36be5b" xlink:href="nktr-20220630.xsd#nktr_EmployeeSeveranceWithNoServicePeriodMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeSeveranceMember_e1c9d471-f509-4494-a0fd-d4c225d18e92" xlink:to="loc_nktr_EmployeeSeveranceWithNoServicePeriodMember_2bba9c3a-a776-4553-896b-9a209e36be5b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_EmployeeSeveranceWithServicePeriodRequirementMember_dd8580ef-61a7-4272-823b-15b28b859cb6" xlink:href="nktr-20220630.xsd#nktr_EmployeeSeveranceWithServicePeriodRequirementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeSeveranceMember_e1c9d471-f509-4494-a0fd-d4c225d18e92" xlink:to="loc_nktr_EmployeeSeveranceWithServicePeriodRequirementMember_dd8580ef-61a7-4272-823b-15b28b859cb6" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.nektar.com/role/RestructuringImpairmentandOtherCostsofTerminatedProgramSubleaseInformationDetails" xlink:type="simple" xlink:href="nktr-20220630.xsd#RestructuringImpairmentandOtherCostsofTerminatedProgramSubleaseInformationDetails"/>
  <link:definitionLink xlink:role="http://www.nektar.com/role/RestructuringImpairmentandOtherCostsofTerminatedProgramSubleaseInformationDetails" xlink:type="extended" id="iff11260b90594ec1b62758c2874622d8_RestructuringImpairmentandOtherCostsofTerminatedProgramSubleaseInformationDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveLineItems_d0264f8f-4dd5-41dc-978b-4e6ece4928b8" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestructuringCostAndReserveLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_PropertyPlantAndEquipmentAndOperatingLeaseRightOfUseAssetFairValueDisclosure_5a33b87a-c2bf-4206-adbc-3a3095329583" xlink:href="nktr-20220630.xsd#nktr_PropertyPlantAndEquipmentAndOperatingLeaseRightOfUseAssetFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_d0264f8f-4dd5-41dc-978b-4e6ece4928b8" xlink:to="loc_nktr_PropertyPlantAndEquipmentAndOperatingLeaseRightOfUseAssetFairValueDisclosure_5a33b87a-c2bf-4206-adbc-3a3095329583" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseImpairmentLoss_29df4b04-544b-469e-ad01-4bf77afd5665" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingLeaseImpairmentLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_d0264f8f-4dd5-41dc-978b-4e6ece4928b8" xlink:to="loc_us-gaap_OperatingLeaseImpairmentLoss_29df4b04-544b-469e-ad01-4bf77afd5665" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ImpairmentOfLongLivedAssetsHeldForUse_52b9dbec-76dc-448c-982b-86363cba6b44" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ImpairmentOfLongLivedAssetsHeldForUse"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_d0264f8f-4dd5-41dc-978b-4e6ece4928b8" xlink:to="loc_us-gaap_ImpairmentOfLongLivedAssetsHeldForUse_52b9dbec-76dc-448c-982b-86363cba6b44" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetImpairmentCharges_1383d2da-e3fa-4778-98f8-f72c4ef84684" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AssetImpairmentCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_d0264f8f-4dd5-41dc-978b-4e6ece4928b8" xlink:to="loc_us-gaap_AssetImpairmentCharges_1383d2da-e3fa-4778-98f8-f72c4ef84684" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_ab7fd98e-cfd9-44e7-b274-848f0f4ef9b5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfRestructuringAndRelatedCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_d0264f8f-4dd5-41dc-978b-4e6ece4928b8" xlink:to="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_ab7fd98e-cfd9-44e7-b274-848f0f4ef9b5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_7817a0c5-efc2-420e-a9fd-98c2777586bb" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_ab7fd98e-cfd9-44e7-b274-848f0f4ef9b5" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_7817a0c5-efc2-420e-a9fd-98c2777586bb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_7817a0c5-efc2-420e-a9fd-98c2777586bb_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_7817a0c5-efc2-420e-a9fd-98c2777586bb" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_7817a0c5-efc2-420e-a9fd-98c2777586bb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_0a39282b-3de7-491e-b0c1-ad2eecfb8f43" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_7817a0c5-efc2-420e-a9fd-98c2777586bb" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_0a39282b-3de7-491e-b0c1-ad2eecfb8f43" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_8e8c2846-9a53-4113-af50-17b760ad317e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_0a39282b-3de7-491e-b0c1-ad2eecfb8f43" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_8e8c2846-9a53-4113-af50-17b760ad317e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByAssetClassAxis_b9160259-578f-4e86-8d9b-9ce5d6ef6075" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByAssetClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_ab7fd98e-cfd9-44e7-b274-848f0f4ef9b5" xlink:to="loc_us-gaap_FairValueByAssetClassAxis_b9160259-578f-4e86-8d9b-9ce5d6ef6075" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_b9160259-578f-4e86-8d9b-9ce5d6ef6075_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_b9160259-578f-4e86-8d9b-9ce5d6ef6075" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_b9160259-578f-4e86-8d9b-9ce5d6ef6075_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_e6685993-ab2b-46b6-96c4-426f443c5597" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_b9160259-578f-4e86-8d9b-9ce5d6ef6075" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_e6685993-ab2b-46b6-96c4-426f443c5597" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_SubleasePropertyPlantAndEquipmentMember_ac1a79c0-dcf0-43d0-bbd1-a39677ba5892" xlink:href="nktr-20220630.xsd#nktr_SubleasePropertyPlantAndEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_e6685993-ab2b-46b6-96c4-426f443c5597" xlink:to="loc_nktr_SubleasePropertyPlantAndEquipmentMember_ac1a79c0-dcf0-43d0-bbd1-a39677ba5892" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_SubleaseOperatingLeaseRightOfUseAssetsMember_e6636a11-9d91-4292-bb67-a6e07e9e3eb5" xlink:href="nktr-20220630.xsd#nktr_SubleaseOperatingLeaseRightOfUseAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_e6685993-ab2b-46b6-96c4-426f443c5597" xlink:to="loc_nktr_SubleaseOperatingLeaseRightOfUseAssetsMember_e6636a11-9d91-4292-bb67-a6e07e9e3eb5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementBasisAxis_7d747a17-2d02-459e-beb7-9e739cce9330" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByMeasurementBasisAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_ab7fd98e-cfd9-44e7-b274-848f0f4ef9b5" xlink:to="loc_us-gaap_FairValueByMeasurementBasisAxis_7d747a17-2d02-459e-beb7-9e739cce9330" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_7d747a17-2d02-459e-beb7-9e739cce9330_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_7d747a17-2d02-459e-beb7-9e739cce9330" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_7d747a17-2d02-459e-beb7-9e739cce9330_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueDisclosureItemAmountsDomain_d8b788cf-7d61-410b-b5b8-a2ce034b4320" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueDisclosureItemAmountsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_7d747a17-2d02-459e-beb7-9e739cce9330" xlink:to="loc_us-gaap_FairValueDisclosureItemAmountsDomain_d8b788cf-7d61-410b-b5b8-a2ce034b4320" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_90037dd4-b2b4-4dfd-802e-fd3977051792" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_d8b788cf-7d61-410b-b5b8-a2ce034b4320" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_90037dd4-b2b4-4dfd-802e-fd3977051792" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_33e0d7fd-d6a8-4cda-89e1-3001bfee8d14" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CarryingReportedAmountFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_90037dd4-b2b4-4dfd-802e-fd3977051792" xlink:to="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_33e0d7fd-d6a8-4cda-89e1-3001bfee8d14" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_3dd3b324-bd27-4b9f-bdfc-db495dd755ba" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EstimateOfFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_90037dd4-b2b4-4dfd-802e-fd3977051792" xlink:to="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_3dd3b324-bd27-4b9f-bdfc-db495dd755ba" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.nektar.com/role/RestructuringImpairmentandOtherCostsofTerminatedProgramScheduleofPropertyPlantandEquipmentDetails" xlink:type="simple" xlink:href="nktr-20220630.xsd#RestructuringImpairmentandOtherCostsofTerminatedProgramScheduleofPropertyPlantandEquipmentDetails"/>
  <link:definitionLink xlink:role="http://www.nektar.com/role/RestructuringImpairmentandOtherCostsofTerminatedProgramScheduleofPropertyPlantandEquipmentDetails" xlink:type="extended" id="i132ce68425974d56a21297c6492bb53f_RestructuringImpairmentandOtherCostsofTerminatedProgramScheduleofPropertyPlantandEquipmentDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_177bca82-95b0-45f3-bbe2-eddea28d1063" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentGross_2536e92e-66d2-4939-9f9b-842f847d8f59" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_177bca82-95b0-45f3-bbe2-eddea28d1063" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentGross_2536e92e-66d2-4939-9f9b-842f847d8f59" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_a7344f35-71dc-4952-98ca-fc629d00ce45" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_177bca82-95b0-45f3-bbe2-eddea28d1063" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_a7344f35-71dc-4952-98ca-fc629d00ce45" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_78946828-fd6b-4368-a61b-a29c44593016" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_177bca82-95b0-45f3-bbe2-eddea28d1063" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_78946828-fd6b-4368-a61b-a29c44593016" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_3ffc1184-12c0-4c60-9365-4a25bc40ef30" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_177bca82-95b0-45f3-bbe2-eddea28d1063" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_3ffc1184-12c0-4c60-9365-4a25bc40ef30" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_22aa4972-b7c9-45f0-a6ed-02739216eba4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_3ffc1184-12c0-4c60-9365-4a25bc40ef30" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_22aa4972-b7c9-45f0-a6ed-02739216eba4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_22aa4972-b7c9-45f0-a6ed-02739216eba4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_22aa4972-b7c9-45f0-a6ed-02739216eba4" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_22aa4972-b7c9-45f0-a6ed-02739216eba4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_5cf09f27-5d6b-49ca-b146-e41ada169d41" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_22aa4972-b7c9-45f0-a6ed-02739216eba4" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_5cf09f27-5d6b-49ca-b146-e41ada169d41" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_BuildingAndLeaseholdImprovementsMember_5e064e8f-3676-4ddd-9121-1af045ff3009" xlink:href="nktr-20220630.xsd#nktr_BuildingAndLeaseholdImprovementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_5cf09f27-5d6b-49ca-b146-e41ada169d41" xlink:to="loc_nktr_BuildingAndLeaseholdImprovementsMember_5e064e8f-3676-4ddd-9121-1af045ff3009" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_LaboratoryEquipmentMember_c7fcee66-4c7c-41a8-9415-96b1a671ad9b" xlink:href="nktr-20220630.xsd#nktr_LaboratoryEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_5cf09f27-5d6b-49ca-b146-e41ada169d41" xlink:to="loc_nktr_LaboratoryEquipmentMember_c7fcee66-4c7c-41a8-9415-96b1a671ad9b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_ComputerEquipmentAndSoftwareMember_a75653eb-a9b3-4a52-9d4f-e2e39e299573" xlink:href="nktr-20220630.xsd#nktr_ComputerEquipmentAndSoftwareMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_5cf09f27-5d6b-49ca-b146-e41ada169d41" xlink:to="loc_nktr_ComputerEquipmentAndSoftwareMember_a75653eb-a9b3-4a52-9d4f-e2e39e299573" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquipmentMember_7f877244-0ade-4e1d-b65c-7b40fe844a7f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_5cf09f27-5d6b-49ca-b146-e41ada169d41" xlink:to="loc_us-gaap_EquipmentMember_7f877244-0ade-4e1d-b65c-7b40fe844a7f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FurnitureAndFixturesMember_2e31d410-ce57-4298-b1f6-b69622518eeb" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FurnitureAndFixturesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_5cf09f27-5d6b-49ca-b146-e41ada169d41" xlink:to="loc_us-gaap_FurnitureAndFixturesMember_2e31d410-ce57-4298-b1f6-b69622518eeb" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_TotalPropertyPlantAndEquipmentExcludingConstructionInProgressMember_88d851b3-878d-4f6f-8b64-49a2df0a5de3" xlink:href="nktr-20220630.xsd#nktr_TotalPropertyPlantAndEquipmentExcludingConstructionInProgressMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_5cf09f27-5d6b-49ca-b146-e41ada169d41" xlink:to="loc_nktr_TotalPropertyPlantAndEquipmentExcludingConstructionInProgressMember_88d851b3-878d-4f6f-8b64-49a2df0a5de3" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConstructionInProgressMember_616c1ed7-1263-42a5-bf93-9d592751ab2e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConstructionInProgressMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_5cf09f27-5d6b-49ca-b146-e41ada169d41" xlink:to="loc_us-gaap_ConstructionInProgressMember_616c1ed7-1263-42a5-bf93-9d592751ab2e" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.nektar.com/role/StockBasedCompensationAdditionalInformationDetail" xlink:type="simple" xlink:href="nktr-20220630.xsd#StockBasedCompensationAdditionalInformationDetail"/>
  <link:definitionLink xlink:role="http://www.nektar.com/role/StockBasedCompensationAdditionalInformationDetail" xlink:type="extended" id="i4669f52ad15c437697dd085c495c272d_StockBasedCompensationAdditionalInformationDetail">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_de69ea60-2db0-450e-8c4c-b98ba170ebf3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_b4daf8b4-e3b7-4a08-a15c-1eebfa773e34" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_de69ea60-2db0-450e-8c4c-b98ba170ebf3" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_b4daf8b4-e3b7-4a08-a15c-1eebfa773e34" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_7d75cb61-9178-4428-916e-9ec0eadf785f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_de69ea60-2db0-450e-8c4c-b98ba170ebf3" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_7d75cb61-9178-4428-916e-9ec0eadf785f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_1c1a3b52-54fd-4dc9-b1df-4834ead4de78" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_7d75cb61-9178-4428-916e-9ec0eadf785f" xlink:to="loc_us-gaap_PlanNameAxis_1c1a3b52-54fd-4dc9-b1df-4834ead4de78" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_1c1a3b52-54fd-4dc9-b1df-4834ead4de78_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_1c1a3b52-54fd-4dc9-b1df-4834ead4de78" xlink:to="loc_us-gaap_PlanNameDomain_1c1a3b52-54fd-4dc9-b1df-4834ead4de78_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_6f6bd63d-99d2-4d24-9320-999a4b9aed77" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_1c1a3b52-54fd-4dc9-b1df-4834ead4de78" xlink:to="loc_us-gaap_PlanNameDomain_6f6bd63d-99d2-4d24-9320-999a4b9aed77" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_TwoThousandSeventeenPerformanceIncentivePlanMember_85029996-f1f5-48be-881b-33e803beea7b" xlink:href="nktr-20220630.xsd#nktr_TwoThousandSeventeenPerformanceIncentivePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_6f6bd63d-99d2-4d24-9320-999a4b9aed77" xlink:to="loc_nktr_TwoThousandSeventeenPerformanceIncentivePlanMember_85029996-f1f5-48be-881b-33e803beea7b" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.nektar.com/role/StockBasedCompensationStockBasedCompensationExpenseDetail" xlink:type="simple" xlink:href="nktr-20220630.xsd#StockBasedCompensationStockBasedCompensationExpenseDetail"/>
  <link:definitionLink xlink:role="http://www.nektar.com/role/StockBasedCompensationStockBasedCompensationExpenseDetail" xlink:type="extended" id="i24952d4b7e03425eadc44644d67721b5_StockBasedCompensationStockBasedCompensationExpenseDetail">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_46ad7242-8132-4d1a-b635-6990b0f7859b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_edf160d5-8937-41a3-bfad-3e82c0f157c8" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_46ad7242-8132-4d1a-b635-6990b0f7859b" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_edf160d5-8937-41a3-bfad-3e82c0f157c8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_65a2752c-2a7b-4623-a2e7-e36638d6761a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_46ad7242-8132-4d1a-b635-6990b0f7859b" xlink:to="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_65a2752c-2a7b-4623-a2e7-e36638d6761a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_810938c2-9ae3-4d13-86f2-72c865ba75bd" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_65a2752c-2a7b-4623-a2e7-e36638d6761a" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_810938c2-9ae3-4d13-86f2-72c865ba75bd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_810938c2-9ae3-4d13-86f2-72c865ba75bd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_810938c2-9ae3-4d13-86f2-72c865ba75bd" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_810938c2-9ae3-4d13-86f2-72c865ba75bd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_d0b0f10e-4b77-4020-ba13-c8c0a1ecea78" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_810938c2-9ae3-4d13-86f2-72c865ba75bd" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_d0b0f10e-4b77-4020-ba13-c8c0a1ecea78" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfSalesMember_f5a1457c-0d24-45d1-8bf5-90f21ce4bc48" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CostOfSalesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_d0b0f10e-4b77-4020-ba13-c8c0a1ecea78" xlink:to="loc_us-gaap_CostOfSalesMember_f5a1457c-0d24-45d1-8bf5-90f21ce4bc48" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpenseMember_cc0602a3-5013-4bd9-b33c-dff8984c6b0d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ResearchAndDevelopmentExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_d0b0f10e-4b77-4020-ba13-c8c0a1ecea78" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpenseMember_cc0602a3-5013-4bd9-b33c-dff8984c6b0d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpenseMember_dc0e9ef4-0db8-4194-81ce-70691da4e84e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_GeneralAndAdministrativeExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_d0b0f10e-4b77-4020-ba13-c8c0a1ecea78" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpenseMember_dc0e9ef4-0db8-4194-81ce-70691da4e84e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_nktr_RestructuringImpairmentAndOtherCostsOfTerminatedProgramMember_4630eb52-5175-4281-80fe-d460106824d9" xlink:href="nktr-20220630.xsd#nktr_RestructuringImpairmentAndOtherCostsOfTerminatedProgramMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_d0b0f10e-4b77-4020-ba13-c8c0a1ecea78" xlink:to="loc_nktr_RestructuringImpairmentAndOtherCostsOfTerminatedProgramMember_4630eb52-5175-4281-80fe-d460106824d9" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.nektar.com/role/StockBasedCompensationActivityDetail" xlink:type="simple" xlink:href="nktr-20220630.xsd#StockBasedCompensationActivityDetail"/>
  <link:definitionLink xlink:role="http://www.nektar.com/role/StockBasedCompensationActivityDetail" xlink:type="extended" id="i43516139e86e48aabc190b6983b7a2a5_StockBasedCompensationActivityDetail">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_9a32cc2b-f0b5-4569-964d-0be824121643" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod_a4e7d98a-5c5a-4eb5-a9e2-8bfc38cf89c9" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_9a32cc2b-f0b5-4569-964d-0be824121643" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod_a4e7d98a-5c5a-4eb5-a9e2-8bfc38cf89c9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_f6d5b627-f456-4db8-88fd-e328bdd73d7a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_9a32cc2b-f0b5-4569-964d-0be824121643" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_f6d5b627-f456-4db8-88fd-e328bdd73d7a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_9f03465c-02b6-48b4-8a4e-323dae1c91bf" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_9a32cc2b-f0b5-4569-964d-0be824121643" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_9f03465c-02b6-48b4-8a4e-323dae1c91bf" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_42bf2e1c-82e1-4557-b722-98c0ae837126" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_9a32cc2b-f0b5-4569-964d-0be824121643" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_42bf2e1c-82e1-4557-b722-98c0ae837126" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation_c830e5f7-b974-4752-825a-0b8d0de76d73" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_9a32cc2b-f0b5-4569-964d-0be824121643" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation_c830e5f7-b974-4752-825a-0b8d0de76d73" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_afd3afc7-8e65-4908-aba6-ef0ebaf28d5b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_9a32cc2b-f0b5-4569-964d-0be824121643" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_afd3afc7-8e65-4908-aba6-ef0ebaf28d5b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_f14d6077-4240-4932-b7d5-b1e59bfa72f9" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_afd3afc7-8e65-4908-aba6-ef0ebaf28d5b" xlink:to="loc_us-gaap_AwardTypeAxis_f14d6077-4240-4932-b7d5-b1e59bfa72f9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_f14d6077-4240-4932-b7d5-b1e59bfa72f9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_f14d6077-4240-4932-b7d5-b1e59bfa72f9" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_f14d6077-4240-4932-b7d5-b1e59bfa72f9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_cdd76ace-7a26-44c5-83c8-d66876b5de82" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_f14d6077-4240-4932-b7d5-b1e59bfa72f9" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_cdd76ace-7a26-44c5-83c8-d66876b5de82" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_74886365-0670-4e2f-9127-32eb42002c63" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_cdd76ace-7a26-44c5-83c8-d66876b5de82" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_74886365-0670-4e2f-9127-32eb42002c63" xlink:type="arc" order="0"/>
  </link:definitionLink>
</link:linkbase>
