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

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:019febef-ec8b-7848-9dab-6c8058dd174b,g:a85e85ad-7918-447e-b5a5-7da0f28fe27a-->
<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://roivant.com/role/CondensedConsolidatedStatementsofOperations" xlink:type="simple" xlink:href="roiv-20260930.xsd#CondensedConsolidatedStatementsofOperations"/>
  <link:definitionLink xlink:role="http://roivant.com/role/CondensedConsolidatedStatementsofOperations" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_01a0a9b3-037f-735f-850d-dec6ebf0055b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_01a0a9b3-037f-717e-86c1-0c450a1b2489" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_01a0a9b3-037f-735f-850d-dec6ebf0055b" xlink:to="loc_us-gaap_StatementTable_01a0a9b3-037f-717e-86c1-0c450a1b2489" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_01a0a9b3-037f-7fa8-a15a-570832f06060" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_01a0a9b3-037f-717e-86c1-0c450a1b2489" xlink:to="loc_srt_ProductOrServiceAxis_01a0a9b3-037f-7fa8-a15a-570832f06060" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_01a0a9b3-037f-7fa8-a15a-570832f06060_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_01a0a9b3-037f-7fa8-a15a-570832f06060" xlink:to="loc_srt_ProductsAndServicesDomain_01a0a9b3-037f-7fa8-a15a-570832f06060_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_01a0a9b3-037f-7bde-85c0-c0704f2ea5df" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_01a0a9b3-037f-7fa8-a15a-570832f06060" xlink:to="loc_srt_ProductsAndServicesDomain_01a0a9b3-037f-7bde-85c0-c0704f2ea5df" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductMember_01a0a9b3-037f-7f1a-8817-9cbcf0f15089" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProductMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_01a0a9b3-037f-7bde-85c0-c0704f2ea5df" xlink:to="loc_us-gaap_ProductMember_01a0a9b3-037f-7f1a-8817-9cbcf0f15089" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_LicenseMilestoneAndOtherRevenueMember_01a0f231-2080-73da-8a41-b028913b56d9" xlink:href="roiv-20260930.xsd#roiv_LicenseMilestoneAndOtherRevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_01a0a9b3-037f-7bde-85c0-c0704f2ea5df" xlink:to="loc_roiv_LicenseMilestoneAndOtherRevenueMember_01a0f231-2080-73da-8a41-b028913b56d9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_01a0a9b3-037f-72dc-8fe6-cc848e7b38bd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a0a9b3-037f-735f-850d-dec6ebf0055b" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_01a0a9b3-037f-72dc-8fe6-cc848e7b38bd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfRevenue_01a0a9b6-3ce1-756a-8b0e-480af361f054" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostOfRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a0a9b3-037f-735f-850d-dec6ebf0055b" xlink:to="loc_us-gaap_CostOfRevenue_01a0a9b6-3ce1-756a-8b0e-480af361f054" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpense_01a0a9b6-3ce1-7295-9b1c-96ad3a637c5f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ResearchAndDevelopmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a0a9b3-037f-735f-850d-dec6ebf0055b" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpense_01a0a9b6-3ce1-7295-9b1c-96ad3a637c5f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingGeneralAndAdministrativeExpense_01a0a9b6-3ce1-7145-b2e8-e3e76d43c0dc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SellingGeneralAndAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a0a9b3-037f-735f-850d-dec6ebf0055b" xlink:to="loc_us-gaap_SellingGeneralAndAdministrativeExpense_01a0a9b6-3ce1-7145-b2e8-e3e76d43c0dc" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostsAndExpenses_01a0a9b6-3ce1-7a34-8241-ef75c450e848" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostsAndExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a0a9b3-037f-735f-850d-dec6ebf0055b" xlink:to="loc_us-gaap_CostsAndExpenses_01a0a9b6-3ce1-7a34-8241-ef75c450e848" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LitigationSettlementGain_01a0a9b6-3ce1-7867-ada7-9cb13de49c0b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LitigationSettlementGain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a0a9b3-037f-735f-850d-dec6ebf0055b" xlink:to="loc_us-gaap_LitigationSettlementGain_01a0a9b6-3ce1-7867-ada7-9cb13de49c0b" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_01a0a9b6-3ce1-7d21-86e1-c8bd86aefd13" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a0a9b3-037f-735f-850d-dec6ebf0055b" xlink:to="loc_us-gaap_OperatingIncomeLoss_01a0a9b6-3ce1-7d21-86e1-c8bd86aefd13" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnInvestments_01a0a9b6-3ce1-7f24-9027-ffaed6ebde74" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainLossOnInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a0a9b3-037f-735f-850d-dec6ebf0055b" xlink:to="loc_us-gaap_GainLossOnInvestments_01a0a9b6-3ce1-7f24-9027-ffaed6ebde74" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_GainLossOnFairValueOfLiabilityInstruments_01a0a9b6-3ce1-7ec4-b599-68d759022951" xlink:href="roiv-20260930.xsd#roiv_GainLossOnFairValueOfLiabilityInstruments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a0a9b3-037f-735f-850d-dec6ebf0055b" xlink:to="loc_roiv_GainLossOnFairValueOfLiabilityInstruments_01a0a9b6-3ce1-7ec4-b599-68d759022951" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentIncomeInterest_01a0a9b6-3ce1-768c-9cfe-9b2af6e119b2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentIncomeInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a0a9b3-037f-735f-850d-dec6ebf0055b" xlink:to="loc_us-gaap_InvestmentIncomeInterest_01a0a9b6-3ce1-768c-9cfe-9b2af6e119b2" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_01a0a9b6-3ce1-77a7-a42d-9fc7605d546c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherNonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a0a9b3-037f-735f-850d-dec6ebf0055b" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_01a0a9b6-3ce1-77a7-a42d-9fc7605d546c" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_01a0a9b6-3ce1-7df2-9273-8ec67e63bfac" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a0a9b3-037f-735f-850d-dec6ebf0055b" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_01a0a9b6-3ce1-7df2-9273-8ec67e63bfac" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_01a0a9b6-3ce1-722a-810e-c56e9a257eca" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a0a9b3-037f-735f-850d-dec6ebf0055b" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_01a0a9b6-3ce1-722a-810e-c56e9a257eca" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsIncludingPortionAttributableToNoncontrollingInterest_01a0a9bf-048b-76dc-85de-88dc7675a2dd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromContinuingOperationsIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a0a9b3-037f-735f-850d-dec6ebf0055b" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsIncludingPortionAttributableToNoncontrollingInterest_01a0a9bf-048b-76dc-85de-88dc7675a2dd" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTax_01a0f238-8ee7-7b62-b6b2-374402f92d33" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a0a9b3-037f-735f-850d-dec6ebf0055b" xlink:to="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTax_01a0f238-8ee7-7b62-b6b2-374402f92d33" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_01a0f238-ff6a-78fa-acb3-ae7e8bfc393c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a0a9b3-037f-735f-850d-dec6ebf0055b" xlink:to="loc_us-gaap_ProfitLoss_01a0f238-ff6a-78fa-acb3-ae7e8bfc393c" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAttributableToNoncontrollingInterest_01a0a9b6-3ce1-7075-8c74-c25bc3c9f844" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLossAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a0a9b3-037f-735f-850d-dec6ebf0055b" xlink:to="loc_us-gaap_NetIncomeLossAttributableToNoncontrollingInterest_01a0a9b6-3ce1-7075-8c74-c25bc3c9f844" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_01a0a9b6-3ce1-7780-9e96-8a1fce6178bf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a0a9b3-037f-735f-850d-dec6ebf0055b" xlink:to="loc_us-gaap_NetIncomeLoss_01a0a9b6-3ce1-7780-9e96-8a1fce6178bf" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeAmountsAttributableToReportingEntityDisclosuresAbstract_01a0f263-5fb8-7d55-bbc0-1cae5d463eb1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeAmountsAttributableToReportingEntityDisclosuresAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a0a9b3-037f-735f-850d-dec6ebf0055b" xlink:to="loc_us-gaap_IncomeAmountsAttributableToReportingEntityDisclosuresAbstract_01a0f263-5fb8-7d55-bbc0-1cae5d463eb1" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperations_01a0f239-9d51-7dab-b2f6-df01317c6771" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromContinuingOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeAmountsAttributableToReportingEntityDisclosuresAbstract_01a0f263-5fb8-7d55-bbc0-1cae5d463eb1" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperations_01a0f239-9d51-7dab-b2f6-df01317c6771" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity_01a0f23a-2094-7be5-b0a5-2ef5a2ddfeae" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeAmountsAttributableToReportingEntityDisclosuresAbstract_01a0f263-5fb8-7d55-bbc0-1cae5d463eb1" xlink:to="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity_01a0f23a-2094-7be5-b0a5-2ef5a2ddfeae" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_01a0f264-4370-7526-b482-54f49e5788fe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasicAbstract_01a0f25d-0dbe-71d2-8cd5-4850c7d9f801" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EarningsPerShareBasicAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a0a9b3-037f-735f-850d-dec6ebf0055b" xlink:to="loc_us-gaap_EarningsPerShareBasicAbstract_01a0f25d-0dbe-71d2-8cd5-4850c7d9f801" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsPerDilutedShare_01a177f6-5c63-7061-9374-64c35ddbaf97" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromContinuingOperationsPerDilutedShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicAbstract_01a0f25d-0dbe-71d2-8cd5-4850c7d9f801" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsPerDilutedShare_01a177f6-5c63-7061-9374-64c35ddbaf97" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsPerBasicShare_01a0f23b-7350-70ad-9780-22415fa75d94" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromContinuingOperationsPerBasicShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicAbstract_01a0f25d-0dbe-71d2-8cd5-4850c7d9f801" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsPerBasicShare_01a0f23b-7350-70ad-9780-22415fa75d94" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxPerBasicShare_01a0f23b-bd53-7d83-94d9-b094bb336c3a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxPerBasicShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicAbstract_01a0f25d-0dbe-71d2-8cd5-4850c7d9f801" xlink:to="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxPerBasicShare_01a0f23b-bd53-7d83-94d9-b094bb336c3a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxPerDilutedShare_01a177f6-5c63-77ed-837d-0b619e333921" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxPerDilutedShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicAbstract_01a0f25d-0dbe-71d2-8cd5-4850c7d9f801" xlink:to="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxPerDilutedShare_01a177f6-5c63-77ed-837d-0b619e333921" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasic_01a0a9b6-3ce1-7b29-bb2a-e6db43f428ac" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EarningsPerShareBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicAbstract_01a0f25d-0dbe-71d2-8cd5-4850c7d9f801" xlink:to="loc_us-gaap_EarningsPerShareBasic_01a0a9b6-3ce1-7b29-bb2a-e6db43f428ac" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareDiluted_01a1a585-0ef4-79b8-8d8c-039c9b07c684" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EarningsPerShareDiluted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicAbstract_01a0f25d-0dbe-71d2-8cd5-4850c7d9f801" xlink:to="loc_us-gaap_EarningsPerShareDiluted_01a1a585-0ef4-79b8-8d8c-039c9b07c684" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_01a0f260-73c1-7527-b2c0-9652ba9ea1d5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a0a9b3-037f-735f-850d-dec6ebf0055b" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_01a0f260-73c1-7527-b2c0-9652ba9ea1d5" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_01a0a9b6-3ce1-754c-922b-993088d45220" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_01a0f260-73c1-7527-b2c0-9652ba9ea1d5" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_01a0a9b6-3ce1-754c-922b-993088d45220" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_01a0a9b6-3ce1-7ff7-9133-3dbc048fc6ea" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_01a0f260-73c1-7527-b2c0-9652ba9ea1d5" xlink:to="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_01a0a9b6-3ce1-7ff7-9133-3dbc048fc6ea" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://roivant.com/role/CondensedConsolidatedStatementsofOperationsParenthetical" xlink:type="simple" xlink:href="roiv-20260930.xsd#CondensedConsolidatedStatementsofOperationsParenthetical"/>
  <link:definitionLink xlink:role="http://roivant.com/role/CondensedConsolidatedStatementsofOperationsParenthetical" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019febef-ed28-7bd2-9e87-99f200d81de4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019febef-ed28-7227-bb13-f765c947a8f9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019febef-ed28-7bd2-9e87-99f200d81de4" xlink:to="loc_us-gaap_StatementTable_019febef-ed28-7227-bb13-f765c947a8f9" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019febef-ed28-7a0f-9c9a-58a8ad5b1286" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementOfIncomeLocationBalanceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019febef-ed28-7227-bb13-f765c947a8f9" xlink:to="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019febef-ed28-7a0f-9c9a-58a8ad5b1286" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensation_019febef-ed28-7279-98dc-c5cd2eb28079" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019febef-ed28-7bd2-9e87-99f200d81de4" xlink:to="loc_us-gaap_ShareBasedCompensation_019febef-ed28-7279-98dc-c5cd2eb28079" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://roivant.com/role/CondensedConsolidatedStatementsofOperationsParenthetical_1" xlink:type="simple" xlink:href="roiv-20260930.xsd#CondensedConsolidatedStatementsofOperationsParenthetical_1"/>
  <link:definitionLink xlink:role="http://roivant.com/role/CondensedConsolidatedStatementsofOperationsParenthetical_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019febef-ed28-7bd2-9e87-99f200d81de4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019febef-ed28-7227-bb13-f765c947a8f9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019febef-ed28-7bd2-9e87-99f200d81de4" xlink:to="loc_us-gaap_StatementTable_019febef-ed28-7227-bb13-f765c947a8f9" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensation_019febef-ed28-7279-98dc-c5cd2eb28079" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019febef-ed28-7bd2-9e87-99f200d81de4" xlink:to="loc_us-gaap_ShareBasedCompensation_019febef-ed28-7279-98dc-c5cd2eb28079" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://roivant.com/role/CondensedConsolidatedStatementsofShareholdersEquity" xlink:type="simple" xlink:href="roiv-20260930.xsd#CondensedConsolidatedStatementsofShareholdersEquity"/>
  <link:definitionLink xlink:role="http://roivant.com/role/CondensedConsolidatedStatementsofShareholdersEquity" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019febef-ed28-7feb-84e1-295652d8ab80" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019febef-ed28-71d5-af72-7f5721663029" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019febef-ed28-7feb-84e1-295652d8ab80" xlink:to="loc_us-gaap_StatementTable_019febef-ed28-71d5-af72-7f5721663029" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019febef-ed28-7f3a-a763-d84b069470a0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019febef-ed28-71d5-af72-7f5721663029" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019febef-ed28-7f3a-a763-d84b069470a0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019febef-ed28-7f3a-a763-d84b069470a0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019febef-ed28-7f3a-a763-d84b069470a0" xlink:to="loc_us-gaap_EquityComponentDomain_019febef-ed28-7f3a-a763-d84b069470a0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019febef-ed28-7acd-9a2a-84ea1f8d748a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019febef-ed28-7f3a-a763-d84b069470a0" xlink:to="loc_us-gaap_EquityComponentDomain_019febef-ed28-7acd-9a2a-84ea1f8d748a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019febef-ed28-7674-a1fd-2cf1f1334e98" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019febef-ed28-7acd-9a2a-84ea1f8d748a" xlink:to="loc_us-gaap_CommonStockMember_019febef-ed28-7674-a1fd-2cf1f1334e98" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_019febef-ed28-769b-9bd5-2edc00993c4a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019febef-ed28-7acd-9a2a-84ea1f8d748a" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_019febef-ed28-769b-9bd5-2edc00993c4a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019febef-ed28-7e20-bf8f-aca63ca8f06c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019febef-ed28-7acd-9a2a-84ea1f8d748a" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019febef-ed28-7e20-bf8f-aca63ca8f06c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_019febef-ed28-7b04-8b82-7515f5013d75" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019febef-ed28-7acd-9a2a-84ea1f8d748a" xlink:to="loc_us-gaap_RetainedEarningsMember_019febef-ed28-7b04-8b82-7515f5013d75" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoncontrollingInterestMember_019febef-ed28-76c7-83f6-aef3f56753f1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NoncontrollingInterestMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019febef-ed28-7acd-9a2a-84ea1f8d748a" xlink:to="loc_us-gaap_NoncontrollingInterestMember_019febef-ed28-76c7-83f6-aef3f56753f1" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019febef-ed28-7631-8b1c-2af7adad8294" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019febef-ed28-7feb-84e1-295652d8ab80" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019febef-ed28-7631-8b1c-2af7adad8294" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019febef-ed28-725d-8ee4-75743bf2ab9f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019febef-ed28-7631-8b1c-2af7adad8294" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_019febef-ed28-725d-8ee4-75743bf2ab9f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019febef-ed28-758b-9503-ba9d34afed1b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019febef-ed28-7631-8b1c-2af7adad8294" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019febef-ed28-758b-9503-ba9d34afed1b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_StockIssuedDuringPeriodSharesInConnectionWithEquityIncentivePlansAndTaxWithholdingPayments_019febef-ed28-7251-9692-dd866482893c" xlink:href="roiv-20260930.xsd#roiv_StockIssuedDuringPeriodSharesInConnectionWithEquityIncentivePlansAndTaxWithholdingPayments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019febef-ed28-7631-8b1c-2af7adad8294" xlink:to="loc_roiv_StockIssuedDuringPeriodSharesInConnectionWithEquityIncentivePlansAndTaxWithholdingPayments_019febef-ed28-7251-9692-dd866482893c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_StockIssuedDuringPeriodValueInConnectionWithEquityIncentivePlansAndTaxWithholdingPayments_019febef-ed28-7a7c-a991-5c8bca648bee" xlink:href="roiv-20260930.xsd#roiv_StockIssuedDuringPeriodValueInConnectionWithEquityIncentivePlansAndTaxWithholdingPayments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019febef-ed28-7631-8b1c-2af7adad8294" xlink:to="loc_roiv_StockIssuedDuringPeriodValueInConnectionWithEquityIncentivePlansAndTaxWithholdingPayments_019febef-ed28-7a7c-a991-5c8bca648bee" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_ExerciseAndVestingOfSubsidiaryShareBasedAwards_019febef-ed28-706b-9cfc-f312b8416454" xlink:href="roiv-20260930.xsd#roiv_ExerciseAndVestingOfSubsidiaryShareBasedAwards"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019febef-ed28-7631-8b1c-2af7adad8294" xlink:to="loc_roiv_ExerciseAndVestingOfSubsidiaryShareBasedAwards_019febef-ed28-706b-9cfc-f312b8416454" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_IssuanceOfSubsidiaryCommonSharesToTheCompanyAndCapitalContributionsToSubsidiaries_019febef-ed28-753d-9357-50a04ac47cc7" xlink:href="roiv-20260930.xsd#roiv_IssuanceOfSubsidiaryCommonSharesToTheCompanyAndCapitalContributionsToSubsidiaries"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019febef-ed28-7631-8b1c-2af7adad8294" xlink:to="loc_roiv_IssuanceOfSubsidiaryCommonSharesToTheCompanyAndCapitalContributionsToSubsidiaries_019febef-ed28-753d-9357-50a04ac47cc7" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedAndRetiredDuringPeriodShares_019febef-ed28-737a-9131-dc138855a968" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockRepurchasedAndRetiredDuringPeriodShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019febef-ed28-7631-8b1c-2af7adad8294" xlink:to="loc_us-gaap_StockRepurchasedAndRetiredDuringPeriodShares_019febef-ed28-737a-9131-dc138855a968" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedAndRetiredDuringPeriodValue_019febef-ed28-7270-bd81-f3e0edbdacdf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockRepurchasedAndRetiredDuringPeriodValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019febef-ed28-7631-8b1c-2af7adad8294" xlink:to="loc_us-gaap_StockRepurchasedAndRetiredDuringPeriodValue_019febef-ed28-7270-bd81-f3e0edbdacdf" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_01a01eda-5243-7270-8685-91e6ec22ead4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019febef-ed28-7631-8b1c-2af7adad8294" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_01a01eda-5243-7270-8685-91e6ec22ead4" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan_019febef-ed28-7533-b2b0-831120ba1842" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019febef-ed28-7631-8b1c-2af7adad8294" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan_019febef-ed28-7533-b2b0-831120ba1842" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_019febef-ed28-75b1-a348-5e7c87a58fb7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019febef-ed28-7631-8b1c-2af7adad8294" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_019febef-ed28-75b1-a348-5e7c87a58fb7" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax_019febef-ed28-7ac1-9d86-96eb6a74e7ef" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019febef-ed28-7631-8b1c-2af7adad8294" xlink:to="loc_us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax_019febef-ed28-7ac1-9d86-96eb6a74e7ef" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentNetOfTaxPortionAttributableToParent_019febef-ed28-7e07-96f2-f9033f0675c1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentNetOfTaxPortionAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019febef-ed28-7631-8b1c-2af7adad8294" xlink:to="loc_us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentNetOfTaxPortionAttributableToParent_019febef-ed28-7e07-96f2-f9033f0675c1" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_ProceedsFromCashContributionsToMajorityOwnedSubsidiaries_019febef-ed28-73c6-be32-4c341e279a7d" xlink:href="roiv-20260930.xsd#roiv_ProceedsFromCashContributionsToMajorityOwnedSubsidiaries"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019febef-ed28-7631-8b1c-2af7adad8294" xlink:to="loc_roiv_ProceedsFromCashContributionsToMajorityOwnedSubsidiaries_019febef-ed28-73c6-be32-4c341e279a7d" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders_01a17801-ddef-7056-882d-c2692ca62463" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019febef-ed28-7631-8b1c-2af7adad8294" xlink:to="loc_us-gaap_MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders_01a17801-ddef-7056-882d-c2692ca62463" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationFromAociCurrentPeriodNetOfTaxAttributableToParent_01a18797-9dd7-7eb7-825a-711f803fb7cf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReclassificationFromAociCurrentPeriodNetOfTaxAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019febef-ed28-7631-8b1c-2af7adad8294" xlink:to="loc_us-gaap_ReclassificationFromAociCurrentPeriodNetOfTaxAttributableToParent_01a18797-9dd7-7eb7-825a-711f803fb7cf" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_019febef-ed28-7414-a051-3c0d4ee4ec18" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019febef-ed28-7631-8b1c-2af7adad8294" xlink:to="loc_us-gaap_ProfitLoss_019febef-ed28-7414-a051-3c0d4ee4ec18" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019febef-ed28-72b3-826f-bb29b4b35ca1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_019febef-ed28-7f79-b9dd-92882ab0d630" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://roivant.com/role/SummaryofSignificantAccountingPoliciesNarrativeDetails" xlink:type="simple" xlink:href="roiv-20260930.xsd#SummaryofSignificantAccountingPoliciesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://roivant.com/role/SummaryofSignificantAccountingPoliciesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductInformationLineItems_01a153f5-fc95-792c-bbf1-c50e13c4345d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProductInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfProductInformationTable_01a153f5-fc95-7173-af2c-3a5484ccee03" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfProductInformationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ProductInformationLineItems_01a153f5-fc95-792c-bbf1-c50e13c4345d" xlink:to="loc_us-gaap_ScheduleOfProductInformationTable_01a153f5-fc95-7173-af2c-3a5484ccee03" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MajorCustomersAxis_01a153f5-fc95-7692-9bfa-9e43fdb594c0" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MajorCustomersAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfProductInformationTable_01a153f5-fc95-7173-af2c-3a5484ccee03" xlink:to="loc_srt_MajorCustomersAxis_01a153f5-fc95-7692-9bfa-9e43fdb594c0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_01a153f5-fc95-7692-9bfa-9e43fdb594c0_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MajorCustomersAxis_01a153f5-fc95-7692-9bfa-9e43fdb594c0" xlink:to="loc_srt_NameOfMajorCustomerDomain_01a153f5-fc95-7692-9bfa-9e43fdb594c0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_01a153f5-fc95-7eac-bd7b-19fa0ee66313" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MajorCustomersAxis_01a153f5-fc95-7692-9bfa-9e43fdb594c0" xlink:to="loc_srt_NameOfMajorCustomerDomain_01a153f5-fc95-7eac-bd7b-19fa0ee66313" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_CustomerAMember_01a153f5-fc95-71a5-b665-9634a220606d" xlink:href="roiv-20260930.xsd#roiv_CustomerAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_01a153f5-fc95-7eac-bd7b-19fa0ee66313" xlink:to="loc_roiv_CustomerAMember_01a153f5-fc95-71a5-b665-9634a220606d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_CustomerBMember_01a153f5-fc95-7386-a0f8-212527e108e9" xlink:href="roiv-20260930.xsd#roiv_CustomerBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_01a153f5-fc95-7eac-bd7b-19fa0ee66313" xlink:to="loc_roiv_CustomerBMember_01a153f5-fc95-7386-a0f8-212527e108e9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_01a153f5-fc95-70b4-8986-6457b427c110" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfProductInformationTable_01a153f5-fc95-7173-af2c-3a5484ccee03" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_01a153f5-fc95-70b4-8986-6457b427c110" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a153f5-fc95-70b4-8986-6457b427c110_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_01a153f5-fc95-70b4-8986-6457b427c110" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a153f5-fc95-70b4-8986-6457b427c110_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a153f5-fc95-7aa6-b698-d66dbc1894ab" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_01a153f5-fc95-70b4-8986-6457b427c110" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a153f5-fc95-7aa6-b698-d66dbc1894ab" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableMember_01a153f5-fc95-70dc-9a4f-6ee36482f390" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsReceivableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a153f5-fc95-7aa6-b698-d66dbc1894ab" xlink:to="loc_us-gaap_AccountsReceivableMember_01a153f5-fc95-70dc-9a4f-6ee36482f390" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_01a153f5-fc95-7dbc-9371-9809504f8ad1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfProductInformationTable_01a153f5-fc95-7173-af2c-3a5484ccee03" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_01a153f5-fc95-7dbc-9371-9809504f8ad1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_01a153f5-fc95-7dbc-9371-9809504f8ad1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_01a153f5-fc95-7dbc-9371-9809504f8ad1" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_01a153f5-fc95-7dbc-9371-9809504f8ad1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_01a153f5-fc95-7f02-822d-26910759490d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_01a153f5-fc95-7dbc-9371-9809504f8ad1" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_01a153f5-fc95-7f02-822d-26910759490d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerConcentrationRiskMember_01a153f5-fc95-7c36-8bad-13e15674cd48" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CustomerConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_01a153f5-fc95-7f02-822d-26910759490d" xlink:to="loc_us-gaap_CustomerConcentrationRiskMember_01a153f5-fc95-7c36-8bad-13e15674cd48" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_01a153e2-9d71-7024-b52c-863d4e062ae8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductInformationLineItems_01a153f5-fc95-792c-bbf1-c50e13c4345d" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_01a153e2-9d71-7024-b52c-863d4e062ae8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfOperatingSegments_019febef-ed28-7197-82b0-481449e5ab71" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NumberOfOperatingSegments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductInformationLineItems_01a153f5-fc95-792c-bbf1-c50e13c4345d" xlink:to="loc_us-gaap_NumberOfOperatingSegments_019febef-ed28-7197-82b0-481449e5ab71" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfReportableSegments_019febef-ed28-726c-854c-13cbac12abc2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NumberOfReportableSegments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductInformationLineItems_01a153f5-fc95-792c-bbf1-c50e13c4345d" xlink:to="loc_us-gaap_NumberOfReportableSegments_019febef-ed28-726c-854c-13cbac12abc2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignCurrencyTransactionGainBeforeTax_019febef-ed28-7ba7-ae91-69eb3745a7a7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ForeignCurrencyTransactionGainBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductInformationLineItems_01a153f5-fc95-792c-bbf1-c50e13c4345d" xlink:to="loc_us-gaap_ForeignCurrencyTransactionGainBeforeTax_019febef-ed28-7ba7-ae91-69eb3745a7a7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignCurrencyTransactionLossBeforeTax_019febef-ed28-7514-ab04-37ffc49d3b14" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ForeignCurrencyTransactionLossBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductInformationLineItems_01a153f5-fc95-792c-bbf1-c50e13c4345d" xlink:to="loc_us-gaap_ForeignCurrencyTransactionLossBeforeTax_019febef-ed28-7514-ab04-37ffc49d3b14" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://roivant.com/role/SummaryofSignificantAccountingPoliciesSchedulesofConcentrationofRiskByCustomersDetails" xlink:type="simple" xlink:href="roiv-20260930.xsd#SummaryofSignificantAccountingPoliciesSchedulesofConcentrationofRiskByCustomersDetails"/>
  <link:definitionLink xlink:role="http://roivant.com/role/SummaryofSignificantAccountingPoliciesSchedulesofConcentrationofRiskByCustomersDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductInformationLineItems_01a153db-5647-75c4-a162-b8aef60b51db" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProductInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfProductInformationTable_01a153db-5647-7a5b-8f37-ef60a5d9b25a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfProductInformationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ProductInformationLineItems_01a153db-5647-75c4-a162-b8aef60b51db" xlink:to="loc_us-gaap_ScheduleOfProductInformationTable_01a153db-5647-7a5b-8f37-ef60a5d9b25a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MajorCustomersAxis_01a153db-5647-748d-af29-bdcac4a8befe" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MajorCustomersAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfProductInformationTable_01a153db-5647-7a5b-8f37-ef60a5d9b25a" xlink:to="loc_srt_MajorCustomersAxis_01a153db-5647-748d-af29-bdcac4a8befe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_01a153db-5647-748d-af29-bdcac4a8befe_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MajorCustomersAxis_01a153db-5647-748d-af29-bdcac4a8befe" xlink:to="loc_srt_NameOfMajorCustomerDomain_01a153db-5647-748d-af29-bdcac4a8befe_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_01a153db-5647-7be3-abfe-be29ac1ebf70" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MajorCustomersAxis_01a153db-5647-748d-af29-bdcac4a8befe" xlink:to="loc_srt_NameOfMajorCustomerDomain_01a153db-5647-7be3-abfe-be29ac1ebf70" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_CustomerAMember_01a153db-5647-70cf-8d67-72c74beee1f8" xlink:href="roiv-20260930.xsd#roiv_CustomerAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_01a153db-5647-7be3-abfe-be29ac1ebf70" xlink:to="loc_roiv_CustomerAMember_01a153db-5647-70cf-8d67-72c74beee1f8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_CustomerBMember_01a153db-5647-7c47-9c89-8ebcdabc800d" xlink:href="roiv-20260930.xsd#roiv_CustomerBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_01a153db-5647-7be3-abfe-be29ac1ebf70" xlink:to="loc_roiv_CustomerBMember_01a153db-5647-7c47-9c89-8ebcdabc800d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_01a153db-5647-7a94-9703-37b4084d5e77" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfProductInformationTable_01a153db-5647-7a5b-8f37-ef60a5d9b25a" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_01a153db-5647-7a94-9703-37b4084d5e77" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a153db-5647-7a94-9703-37b4084d5e77_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_01a153db-5647-7a94-9703-37b4084d5e77" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a153db-5647-7a94-9703-37b4084d5e77_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a153db-5647-75ce-b201-4de91167c12c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_01a153db-5647-7a94-9703-37b4084d5e77" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a153db-5647-75ce-b201-4de91167c12c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerMember_01a153db-5647-74b7-81be-a0273b41ce46" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a153db-5647-75ce-b201-4de91167c12c" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerMember_01a153db-5647-74b7-81be-a0273b41ce46" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableMember_01a153e2-72a6-7a5b-b030-b03bf189d100" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsReceivableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a153db-5647-75ce-b201-4de91167c12c" xlink:to="loc_us-gaap_AccountsReceivableMember_01a153e2-72a6-7a5b-b030-b03bf189d100" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_01a153db-5647-7d4a-aae0-3d9be3001c90" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfProductInformationTable_01a153db-5647-7a5b-8f37-ef60a5d9b25a" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_01a153db-5647-7d4a-aae0-3d9be3001c90" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_01a153db-5647-7d4a-aae0-3d9be3001c90_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_01a153db-5647-7d4a-aae0-3d9be3001c90" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_01a153db-5647-7d4a-aae0-3d9be3001c90_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_01a153db-5647-71d5-82dd-13dc0ac2c044" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_01a153db-5647-7d4a-aae0-3d9be3001c90" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_01a153db-5647-71d5-82dd-13dc0ac2c044" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerConcentrationRiskMember_01a153db-5647-7412-9488-efb548331bf1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CustomerConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_01a153db-5647-71d5-82dd-13dc0ac2c044" xlink:to="loc_us-gaap_CustomerConcentrationRiskMember_01a153db-5647-7412-9488-efb548331bf1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_01a153db-5647-74ee-ac97-961343e0b9da" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductInformationLineItems_01a153db-5647-75c4-a162-b8aef60b51db" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_01a153db-5647-74ee-ac97-961343e0b9da" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://roivant.com/role/CashCashEquivalentsandMarketableSecuritiesScheduleofCashCashEquivalentsandMarketableSecuritiesDetails" xlink:type="simple" xlink:href="roiv-20260930.xsd#CashCashEquivalentsandMarketableSecuritiesScheduleofCashCashEquivalentsandMarketableSecuritiesDetails"/>
  <link:definitionLink xlink:role="http://roivant.com/role/CashCashEquivalentsandMarketableSecuritiesScheduleofCashCashEquivalentsandMarketableSecuritiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MarketableSecuritiesLineItems_019febef-ed28-7afb-9944-9f3444ca70ed" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MarketableSecuritiesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MarketableSecuritiesTable_019febef-ed28-746f-a1ca-3a62c481b775" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MarketableSecuritiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_019febef-ed28-7afb-9944-9f3444ca70ed" xlink:to="loc_us-gaap_MarketableSecuritiesTable_019febef-ed28-746f-a1ca-3a62c481b775" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019febef-ed28-7b2b-a3e9-c1821f66b00c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_MarketableSecuritiesTable_019febef-ed28-746f-a1ca-3a62c481b775" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019febef-ed28-7b2b-a3e9-c1821f66b00c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019febef-ed28-7b2b-a3e9-c1821f66b00c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019febef-ed28-7b2b-a3e9-c1821f66b00c" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019febef-ed28-7b2b-a3e9-c1821f66b00c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019febef-ed28-79a6-b1f7-7d12776b2b5a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019febef-ed28-7b2b-a3e9-c1821f66b00c" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019febef-ed28-79a6-b1f7-7d12776b2b5a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_USTreasurySecuritiesAvailableForSaleMember_019febef-ed28-7039-843d-f8000642c381" xlink:href="roiv-20260930.xsd#roiv_USTreasurySecuritiesAvailableForSaleMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019febef-ed28-79a6-b1f7-7d12776b2b5a" xlink:to="loc_roiv_USTreasurySecuritiesAvailableForSaleMember_019febef-ed28-7039-843d-f8000642c381" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateDebtSecuritiesMember_019febef-ed28-7010-a0b1-ff634be2b4dd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CorporateDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019febef-ed28-79a6-b1f7-7d12776b2b5a" xlink:to="loc_us-gaap_CorporateDebtSecuritiesMember_019febef-ed28-7010-a0b1-ff634be2b4dd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialPaperMember_01a153f8-bb18-7e87-86d4-3a4d14d359a9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommercialPaperMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019febef-ed28-79a6-b1f7-7d12776b2b5a" xlink:to="loc_us-gaap_CommercialPaperMember_01a153f8-bb18-7e87-86d4-3a4d14d359a9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValueAbstract_019febef-ed28-73bf-8448-62373b712238" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValueAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_019febef-ed28-7afb-9944-9f3444ca70ed" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValueAbstract_019febef-ed28-73bf-8448-62373b712238" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Cash_019febef-ed28-7aa1-be9d-928c456cb74a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Cash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashAndCashEquivalentsAtCarryingValueAbstract_019febef-ed28-73bf-8448-62373b712238" xlink:to="loc_us-gaap_Cash_019febef-ed28-7aa1-be9d-928c456cb74a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MoneyMarketFundsAtCarryingValue_019febef-ed28-77a5-abf1-34db3a3215c9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MoneyMarketFundsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashAndCashEquivalentsAtCarryingValueAbstract_019febef-ed28-73bf-8448-62373b712238" xlink:to="loc_us-gaap_MoneyMarketFundsAtCarryingValue_019febef-ed28-77a5-abf1-34db3a3215c9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019febef-ed28-7d3a-b26a-bc5cc21c042e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashAndCashEquivalentsAtCarryingValueAbstract_019febef-ed28-73bf-8448-62373b712238" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019febef-ed28-7d3a-b26a-bc5cc21c042e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MarketableSecuritiesAbstract_019febef-ed28-7408-97b0-acb8402d351f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MarketableSecuritiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_019febef-ed28-7afb-9944-9f3444ca70ed" xlink:to="loc_us-gaap_MarketableSecuritiesAbstract_019febef-ed28-7408-97b0-acb8402d351f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest_019febef-ed28-7e5d-a4e3-afd949145160" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesAbstract_019febef-ed28-7408-97b0-acb8402d351f" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest_019febef-ed28-7e5d-a4e3-afd949145160" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsAndShortTermInvestments_019febef-ed28-7e33-aa2a-f64487d22d29" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashCashEquivalentsAndShortTermInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_019febef-ed28-7afb-9944-9f3444ca70ed" xlink:to="loc_us-gaap_CashCashEquivalentsAndShortTermInvestments_019febef-ed28-7e33-aa2a-f64487d22d29" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://roivant.com/role/CashCashEquivalentsandMarketableSecuritiesScheduleofUnrealizedPositionsforHeldtoMaturitySecuritiesDetails" xlink:type="simple" xlink:href="roiv-20260930.xsd#CashCashEquivalentsandMarketableSecuritiesScheduleofUnrealizedPositionsforHeldtoMaturitySecuritiesDetails"/>
  <link:definitionLink xlink:role="http://roivant.com/role/CashCashEquivalentsandMarketableSecuritiesScheduleofUnrealizedPositionsforHeldtoMaturitySecuritiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MarketableSecuritiesLineItems_019febef-ed28-75cd-b437-e15d4fbe9fbd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MarketableSecuritiesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MarketableSecuritiesTable_019febef-ed28-7be3-8ea4-ad7cdf341b34" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MarketableSecuritiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_019febef-ed28-75cd-b437-e15d4fbe9fbd" xlink:to="loc_us-gaap_MarketableSecuritiesTable_019febef-ed28-7be3-8ea4-ad7cdf341b34" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019febef-ed28-7964-bd7d-eb389ceda2e8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_MarketableSecuritiesTable_019febef-ed28-7be3-8ea4-ad7cdf341b34" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019febef-ed28-7964-bd7d-eb389ceda2e8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019febef-ed28-7964-bd7d-eb389ceda2e8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019febef-ed28-7964-bd7d-eb389ceda2e8" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019febef-ed28-7964-bd7d-eb389ceda2e8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019febef-ed28-708d-993c-0fe6ca60973c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019febef-ed28-7964-bd7d-eb389ceda2e8" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019febef-ed28-708d-993c-0fe6ca60973c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USTreasurySecuritiesMember_019febef-ed28-7d02-b8f7-d8dc97deab39" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_USTreasurySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019febef-ed28-708d-993c-0fe6ca60973c" xlink:to="loc_us-gaap_USTreasurySecuritiesMember_019febef-ed28-7d02-b8f7-d8dc97deab39" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateBondSecuritiesMember_019febef-ed28-7fb0-9781-08c6eef3f850" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CorporateBondSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019febef-ed28-708d-993c-0fe6ca60973c" xlink:to="loc_us-gaap_CorporateBondSecuritiesMember_019febef-ed28-7fb0-9781-08c6eef3f850" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialPaperMember_01a153fb-bc05-7796-b8be-764ce354f677" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommercialPaperMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019febef-ed28-708d-993c-0fe6ca60973c" xlink:to="loc_us-gaap_CommercialPaperMember_01a153fb-bc05-7796-b8be-764ce354f677" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleAmortizedCostExcludingAccruedInterestBeforeAllowanceForCreditLoss_019febef-ed28-72c8-9a47-135894f8dce4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleAmortizedCostExcludingAccruedInterestBeforeAllowanceForCreditLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_019febef-ed28-75cd-b437-e15d4fbe9fbd" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleAmortizedCostExcludingAccruedInterestBeforeAllowanceForCreditLoss_019febef-ed28-72c8-9a47-135894f8dce4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_019febef-ed28-737b-a029-c1a9fffb0cbb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_019febef-ed28-75cd-b437-e15d4fbe9fbd" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_019febef-ed28-737b-a029-c1a9fffb0cbb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_019febef-ed28-7a1f-b3f3-dbcec975bb24" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_019febef-ed28-75cd-b437-e15d4fbe9fbd" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_019febef-ed28-7a1f-b3f3-dbcec975bb24" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest_019febef-ed28-760a-b3f3-455664d6d761" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_019febef-ed28-75cd-b437-e15d4fbe9fbd" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest_019febef-ed28-760a-b3f3-455664d6d761" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestReceivable_019febef-ed28-7ce3-9133-cbcffa203564" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_019febef-ed28-75cd-b437-e15d4fbe9fbd" xlink:to="loc_us-gaap_InterestReceivable_019febef-ed28-7ce3-9133-cbcffa203564" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://roivant.com/role/CashCashEquivalentsandMarketableSecuritiesNarrativeDetails" xlink:type="simple" xlink:href="roiv-20260930.xsd#CashCashEquivalentsandMarketableSecuritiesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://roivant.com/role/CashCashEquivalentsandMarketableSecuritiesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MarketableSecuritiesLineItems_019febef-ed28-780c-ba8d-0e6c47ec23fd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MarketableSecuritiesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MarketableSecuritiesTable_019febef-ed28-73ba-acd1-b07bb3e4ac34" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MarketableSecuritiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_019febef-ed28-780c-ba8d-0e6c47ec23fd" xlink:to="loc_us-gaap_MarketableSecuritiesTable_019febef-ed28-73ba-acd1-b07bb3e4ac34" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019febef-ed28-7beb-840d-8fcca429b62d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_MarketableSecuritiesTable_019febef-ed28-73ba-acd1-b07bb3e4ac34" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019febef-ed28-7beb-840d-8fcca429b62d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019febef-ed28-7beb-840d-8fcca429b62d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019febef-ed28-7beb-840d-8fcca429b62d" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019febef-ed28-7beb-840d-8fcca429b62d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019febef-ed28-7e10-b251-ca70e16ab6a0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019febef-ed28-7beb-840d-8fcca429b62d" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019febef-ed28-7e10-b251-ca70e16ab6a0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_AvailableForSaleMarketableSecuritiesInUnrealizedLossPositionMember_019febef-ed28-7693-83ff-8e1a429e9c32" xlink:href="roiv-20260930.xsd#roiv_AvailableForSaleMarketableSecuritiesInUnrealizedLossPositionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019febef-ed28-7e10-b251-ca70e16ab6a0" xlink:to="loc_roiv_AvailableForSaleMarketableSecuritiesInUnrealizedLossPositionMember_019febef-ed28-7693-83ff-8e1a429e9c32" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_NumberOfDebtSecuritiesAvailableForSale_019febef-ed28-7841-af08-2b00a4d11369" xlink:href="roiv-20260930.xsd#roiv_NumberOfDebtSecuritiesAvailableForSale"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_019febef-ed28-780c-ba8d-0e6c47ec23fd" xlink:to="loc_roiv_NumberOfDebtSecuritiesAvailableForSale_019febef-ed28-7841-af08-2b00a4d11369" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest_019febef-ed28-7974-93f4-18b5c6e162ea" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_019febef-ed28-780c-ba8d-0e6c47ec23fd" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest_019febef-ed28-7974-93f4-18b5c6e162ea" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition_019febef-ed28-73dc-bebd-79aebf3b945d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_019febef-ed28-780c-ba8d-0e6c47ec23fd" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition_019febef-ed28-73dc-bebd-79aebf3b945d" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://roivant.com/role/EquityMethodInvestmentsInvestmentinArbutusDetails" xlink:type="simple" xlink:href="roiv-20260930.xsd#EquityMethodInvestmentsInvestmentinArbutusDetails"/>
  <link:definitionLink xlink:role="http://roivant.com/role/EquityMethodInvestmentsInvestmentinArbutusDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_019febef-ed28-7fb4-a1f1-f97c2d653479" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfEquityMethodInvestmentsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_019febef-ed28-7bbd-bffb-4f7aa14f1144" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfEquityMethodInvestmentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_019febef-ed28-7fb4-a1f1-f97c2d653479" xlink:to="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_019febef-ed28-7bbd-bffb-4f7aa14f1144" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019febef-ed28-7ac8-a9c4-e8be914dd138" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_019febef-ed28-7bbd-bffb-4f7aa14f1144" xlink:to="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019febef-ed28-7ac8-a9c4-e8be914dd138" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_019febef-ed28-7ac8-a9c4-e8be914dd138_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019febef-ed28-7ac8-a9c4-e8be914dd138" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_019febef-ed28-7ac8-a9c4-e8be914dd138_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_019febef-ed28-7c2a-9a90-57fbfc48cc34" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019febef-ed28-7ac8-a9c4-e8be914dd138" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_019febef-ed28-7c2a-9a90-57fbfc48cc34" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_ArbutusBiopharmaCorporationMember_019febef-ed28-75ce-ba6a-050473f21824" xlink:href="roiv-20260930.xsd#roiv_ArbutusBiopharmaCorporationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_019febef-ed28-7c2a-9a90-57fbfc48cc34" xlink:to="loc_roiv_ArbutusBiopharmaCorporationMember_019febef-ed28-75ce-ba6a-050473f21824" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019febef-ed28-73d8-ae57-7263cc155c67" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_019febef-ed28-7bbd-bffb-4f7aa14f1144" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019febef-ed28-73d8-ae57-7263cc155c67" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019febef-ed28-73d8-ae57-7263cc155c67_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019febef-ed28-73d8-ae57-7263cc155c67" xlink:to="loc_us-gaap_EquityComponentDomain_019febef-ed28-73d8-ae57-7263cc155c67_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019febef-ed28-70bb-8f3e-94a0aa7e6965" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019febef-ed28-73d8-ae57-7263cc155c67" xlink:to="loc_us-gaap_EquityComponentDomain_019febef-ed28-70bb-8f3e-94a0aa7e6965" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019febef-ed28-7a0c-a800-105c8b601688" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019febef-ed28-70bb-8f3e-94a0aa7e6965" xlink:to="loc_us-gaap_CommonStockMember_019febef-ed28-7a0c-a800-105c8b601688" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_01a178c0-0adc-7546-ac57-a540ebe057c7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_019febef-ed28-7bbd-bffb-4f7aa14f1144" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_01a178c0-0adc-7546-ac57-a540ebe057c7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_01a178c0-0adc-7546-ac57-a540ebe057c7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_01a178c0-0adc-7546-ac57-a540ebe057c7" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_01a178c0-0adc-7546-ac57-a540ebe057c7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_01a178c0-0adc-79c5-bd88-fc3e28ce6dc6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_01a178c0-0adc-7546-ac57-a540ebe057c7" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_01a178c0-0adc-79c5-bd88-fc3e28ce6dc6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_01a178c0-3c69-7cfc-b837-3fdae2474472" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_01a178c0-0adc-79c5-bd88-fc3e28ce6dc6" xlink:to="loc_us-gaap_SubsequentEventMember_01a178c0-3c69-7cfc-b837-3fdae2474472" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019febef-ed28-7e5f-9ba9-33581fccc51e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_019febef-ed28-7fb4-a1f1-f97c2d653479" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_019febef-ed28-7e5f-9ba9-33581fccc51e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestmentOwnershipPercentage_019febef-ed28-7856-b048-ea69f5b7e4f3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityMethodInvestmentOwnershipPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_019febef-ed28-7fb4-a1f1-f97c2d653479" xlink:to="loc_us-gaap_EquityMethodInvestmentOwnershipPercentage_019febef-ed28-7856-b048-ea69f5b7e4f3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedDuringPeriodShares_01a1540c-065c-7d8d-804a-2b69d50eb6b7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockRepurchasedDuringPeriodShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_019febef-ed28-7fb4-a1f1-f97c2d653479" xlink:to="loc_us-gaap_StockRepurchasedDuringPeriodShares_01a1540c-065c-7d8d-804a-2b69d50eb6b7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedDuringPeriodValue_01a1540c-065c-7521-9de7-2b0b518d1455" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockRepurchasedDuringPeriodValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_019febef-ed28-7fb4-a1f1-f97c2d653479" xlink:to="loc_us-gaap_StockRepurchasedDuringPeriodValue_01a1540c-065c-7521-9de7-2b0b518d1455" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentsFairValueDisclosure_019febef-ed28-7bdb-beef-31ffebb79044" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_019febef-ed28-7fb4-a1f1-f97c2d653479" xlink:to="loc_us-gaap_InvestmentsFairValueDisclosure_019febef-ed28-7bdb-beef-31ffebb79044" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnrealizedGainLossOnInvestments_019febef-ed28-7813-9b67-4ffc092cb277" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UnrealizedGainLossOnInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_019febef-ed28-7fb4-a1f1-f97c2d653479" xlink:to="loc_us-gaap_UnrealizedGainLossOnInvestments_019febef-ed28-7813-9b67-4ffc092cb277" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharePrice_019febef-ed28-7b99-8d76-410973fa2c86" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_019febef-ed28-7fb4-a1f1-f97c2d653479" xlink:to="loc_us-gaap_SharePrice_019febef-ed28-7b99-8d76-410973fa2c86" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://roivant.com/role/EquityMethodInvestmentsInvestmentsinDatavantDetails" xlink:type="simple" xlink:href="roiv-20260930.xsd#EquityMethodInvestmentsInvestmentsinDatavantDetails"/>
  <link:definitionLink xlink:role="http://roivant.com/role/EquityMethodInvestmentsInvestmentsinDatavantDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_019febef-ed28-75ea-853b-69cf0b929071" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfEquityMethodInvestmentsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_019febef-ed28-70e9-8639-5f93879019b9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfEquityMethodInvestmentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_019febef-ed28-75ea-853b-69cf0b929071" xlink:to="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_019febef-ed28-70e9-8639-5f93879019b9" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019febef-ed28-7fd5-9fdd-a9fbab577231" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_019febef-ed28-70e9-8639-5f93879019b9" xlink:to="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019febef-ed28-7fd5-9fdd-a9fbab577231" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_019febef-ed28-7fd5-9fdd-a9fbab577231_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019febef-ed28-7fd5-9fdd-a9fbab577231" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_019febef-ed28-7fd5-9fdd-a9fbab577231_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_019febef-ed28-7996-905c-00219a8cfe02" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019febef-ed28-7fd5-9fdd-a9fbab577231" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_019febef-ed28-7996-905c-00219a8cfe02" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_DatavantMember_019febef-ed28-7899-b07b-b0aca96bc765" xlink:href="roiv-20260930.xsd#roiv_DatavantMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_019febef-ed28-7996-905c-00219a8cfe02" xlink:to="loc_roiv_DatavantMember_019febef-ed28-7899-b07b-b0aca96bc765" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestmentOwnershipPercentage_019febef-ed28-7373-b3ee-65ee3fd03650" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityMethodInvestmentOwnershipPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_019febef-ed28-75ea-853b-69cf0b929071" xlink:to="loc_us-gaap_EquityMethodInvestmentOwnershipPercentage_019febef-ed28-7373-b3ee-65ee3fd03650" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentsFairValueDisclosure_019febef-ed28-73fc-9b68-84e84bde2b39" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_019febef-ed28-75ea-853b-69cf0b929071" xlink:to="loc_us-gaap_InvestmentsFairValueDisclosure_019febef-ed28-73fc-9b68-84e84bde2b39" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnrealizedGainLossOnInvestments_019febef-ed28-7c59-9c29-4e19d6fadabc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UnrealizedGainLossOnInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_019febef-ed28-75ea-853b-69cf0b929071" xlink:to="loc_us-gaap_UnrealizedGainLossOnInvestments_019febef-ed28-7c59-9c29-4e19d6fadabc" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://roivant.com/role/RecentTransactionsandDevelopmentsDetails" xlink:type="simple" xlink:href="roiv-20260930.xsd#RecentTransactionsandDevelopmentsDetails"/>
  <link:definitionLink xlink:role="http://roivant.com/role/RecentTransactionsandDevelopmentsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_01a17848-1926-76f6-b22f-b1f1f475c9ee" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019febef-ed28-73c7-9d3e-7bcfa7677c2a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_01a17848-1926-76f6-b22f-b1f1f475c9ee" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019febef-ed28-73c7-9d3e-7bcfa7677c2a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipAxis_01a17848-364b-738a-ae1f-882a372bd4ef" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_OwnershipAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019febef-ed28-73c7-9d3e-7bcfa7677c2a" xlink:to="loc_srt_OwnershipAxis_01a17848-364b-738a-ae1f-882a372bd4ef" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_01a17848-364b-738a-ae1f-882a372bd4ef_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_OwnershipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_OwnershipAxis_01a17848-364b-738a-ae1f-882a372bd4ef" xlink:to="loc_srt_OwnershipDomain_01a17848-364b-738a-ae1f-882a372bd4ef_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_01a17848-364b-786f-8638-29611040dec7" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_OwnershipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_OwnershipAxis_01a17848-364b-738a-ae1f-882a372bd4ef" xlink:to="loc_srt_OwnershipDomain_01a17848-364b-786f-8638-29611040dec7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_GenevantSciencesLtd.Member_01a17848-364b-7996-a312-6e768b4ced3c" xlink:href="roiv-20260930.xsd#roiv_GenevantSciencesLtd.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_OwnershipDomain_01a17848-364b-786f-8638-29611040dec7" xlink:to="loc_roiv_GenevantSciencesLtd.Member_01a17848-364b-7996-a312-6e768b4ced3c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_01a17848-364b-7b3b-be30-b055492db450" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019febef-ed28-73c7-9d3e-7bcfa7677c2a" xlink:to="loc_dei_LegalEntityAxis_01a17848-364b-7b3b-be30-b055492db450" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_01a17848-364b-7b3b-be30-b055492db450_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_01a17848-364b-7b3b-be30-b055492db450" xlink:to="loc_dei_EntityDomain_01a17848-364b-7b3b-be30-b055492db450_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_01a17848-364b-70fe-aa5a-a433fdec98ca" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_01a17848-364b-7b3b-be30-b055492db450" xlink:to="loc_dei_EntityDomain_01a17848-364b-70fe-aa5a-a433fdec98ca" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_RSLMember_01a17848-364b-7251-876e-3ffd82b513bc" xlink:href="roiv-20260930.xsd#roiv_RSLMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_01a17848-364b-70fe-aa5a-a433fdec98ca" xlink:to="loc_roiv_RSLMember_01a17848-364b-7251-876e-3ffd82b513bc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_ArbutusBiopharmaCorporationMember_01a17848-364b-7363-bb7b-fe07ba2740e5" xlink:href="roiv-20260930.xsd#roiv_ArbutusBiopharmaCorporationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_01a17848-364b-70fe-aa5a-a433fdec98ca" xlink:to="loc_roiv_ArbutusBiopharmaCorporationMember_01a17848-364b-7363-bb7b-fe07ba2740e5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_01a17848-364b-739b-b44e-a8c39e4e4d8b" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019febef-ed28-73c7-9d3e-7bcfa7677c2a" xlink:to="loc_srt_CounterpartyNameAxis_01a17848-364b-739b-b44e-a8c39e4e4d8b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a17848-364b-739b-b44e-a8c39e4e4d8b_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_01a17848-364b-739b-b44e-a8c39e4e4d8b" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a17848-364b-739b-b44e-a8c39e4e4d8b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a17848-364b-702f-9a14-1618c884c4d2" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_01a17848-364b-739b-b44e-a8c39e4e4d8b" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a17848-364b-702f-9a14-1618c884c4d2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_GenevantSciencesGmbHMember_01a17848-364b-7256-bd80-16b53f191e8a" xlink:href="roiv-20260930.xsd#roiv_GenevantSciencesGmbHMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a17848-364b-702f-9a14-1618c884c4d2" xlink:to="loc_roiv_GenevantSciencesGmbHMember_01a17848-364b-7256-bd80-16b53f191e8a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_ArbutusBiopharmaCorporationMember_01a17848-364b-7abd-b651-bdbd8a57b02d" xlink:href="roiv-20260930.xsd#roiv_ArbutusBiopharmaCorporationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a17848-364b-702f-9a14-1618c884c4d2" xlink:to="loc_roiv_ArbutusBiopharmaCorporationMember_01a17848-364b-7abd-b651-bdbd8a57b02d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_ModernaGlobalSettlementMember_01a1784a-15e7-737c-b029-d35ccfe42a1d" xlink:href="roiv-20260930.xsd#roiv_ModernaGlobalSettlementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01a17848-364b-702f-9a14-1618c884c4d2" xlink:to="loc_roiv_ModernaGlobalSettlementMember_01a1784a-15e7-737c-b029-d35ccfe42a1d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_01a17848-62f5-706c-8be9-1cd40e978d89" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019febef-ed28-73c7-9d3e-7bcfa7677c2a" xlink:to="loc_us-gaap_PlanNameAxis_01a17848-62f5-706c-8be9-1cd40e978d89" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_01a17848-62f5-706c-8be9-1cd40e978d89_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_01a17848-62f5-706c-8be9-1cd40e978d89" xlink:to="loc_us-gaap_PlanNameDomain_01a17848-62f5-706c-8be9-1cd40e978d89_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_01a17848-62f5-7826-af14-3ccb25a7fbc0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_01a17848-62f5-706c-8be9-1cd40e978d89" xlink:to="loc_us-gaap_PlanNameDomain_01a17848-62f5-7826-af14-3ccb25a7fbc0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_GSL2018EquityIncentivePlanMember_01a17848-62f5-7113-b00b-83d27a98a3e3" xlink:href="roiv-20260930.xsd#roiv_GSL2018EquityIncentivePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_01a17848-62f5-7826-af14-3ccb25a7fbc0" xlink:to="loc_roiv_GSL2018EquityIncentivePlanMember_01a17848-62f5-7113-b00b-83d27a98a3e3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LitigationSettlementAmountAwardedFromOtherParty_01a17848-1926-7fea-ba87-f825384c89a5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LitigationSettlementAmountAwardedFromOtherParty"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_01a17848-1926-76f6-b22f-b1f1f475c9ee" xlink:to="loc_us-gaap_LitigationSettlementAmountAwardedFromOtherParty_01a17848-1926-7fea-ba87-f825384c89a5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_LitigationSettlementContingentPaymentReceivable_01a17848-1926-7488-98f9-3a04ba9c71e5" xlink:href="roiv-20260930.xsd#roiv_LitigationSettlementContingentPaymentReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_01a17848-1926-76f6-b22f-b1f1f475c9ee" xlink:to="loc_roiv_LitigationSettlementContingentPaymentReceivable_01a17848-1926-7488-98f9-3a04ba9c71e5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_LitigationSettlementNumberOfPatents_01a17848-1926-728f-a1e7-7ac7dde9f1fb" xlink:href="roiv-20260930.xsd#roiv_LitigationSettlementNumberOfPatents"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_01a17848-1926-76f6-b22f-b1f1f475c9ee" xlink:to="loc_roiv_LitigationSettlementNumberOfPatents_01a17848-1926-728f-a1e7-7ac7dde9f1fb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_OwnershipOfSharesPercentage_01a17848-364b-7f17-b1ab-98cddba3ab61" xlink:href="roiv-20260930.xsd#roiv_OwnershipOfSharesPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_01a17848-1926-76f6-b22f-b1f1f475c9ee" xlink:to="loc_roiv_OwnershipOfSharesPercentage_01a17848-364b-7f17-b1ab-98cddba3ab61" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_LitigationSettlementFixedPaymentPercentage_01a17848-364b-74f8-ba76-987cefa4d6b8" xlink:href="roiv-20260930.xsd#roiv_LitigationSettlementFixedPaymentPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_01a17848-1926-76f6-b22f-b1f1f475c9ee" xlink:to="loc_roiv_LitigationSettlementFixedPaymentPercentage_01a17848-364b-74f8-ba76-987cefa4d6b8" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_LitigationSettlementsFixedPaymentReceivable_01a17848-364b-7b3a-8f0a-06c737998cab" xlink:href="roiv-20260930.xsd#roiv_LitigationSettlementsFixedPaymentReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_01a17848-1926-76f6-b22f-b1f1f475c9ee" xlink:to="loc_roiv_LitigationSettlementsFixedPaymentReceivable_01a17848-364b-7b3a-8f0a-06c737998cab" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_LitigationSettlementsReceivableCurrent_01a17848-364b-7c49-822b-aac5b8e83c2a" xlink:href="roiv-20260930.xsd#roiv_LitigationSettlementsReceivableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_01a17848-1926-76f6-b22f-b1f1f475c9ee" xlink:to="loc_roiv_LitigationSettlementsReceivableCurrent_01a17848-364b-7c49-822b-aac5b8e83c2a" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LitigationSettlementGain_01a17848-364b-7365-a453-2f1ba590eb24" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LitigationSettlementGain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_01a17848-1926-76f6-b22f-b1f1f475c9ee" xlink:to="loc_us-gaap_LitigationSettlementGain_01a17848-364b-7365-a453-2f1ba590eb24" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfDividendsCommonStock_01a17848-62f5-766c-b8b4-29da35ec8ecb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsOfDividendsCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_01a17848-1926-76f6-b22f-b1f1f475c9ee" xlink:to="loc_us-gaap_PaymentsOfDividendsCommonStock_01a17848-62f5-766c-b8b4-29da35ec8ecb" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsCash_01a17848-62f5-7394-a484-4e1b52455b67" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DividendsCash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_01a17848-1926-76f6-b22f-b1f1f475c9ee" xlink:to="loc_us-gaap_DividendsCash_01a17848-62f5-7394-a484-4e1b52455b67" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedBonusesCurrent_01a17848-62f5-7a87-b9bc-59c06b23d409" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccruedBonusesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_01a17848-1926-76f6-b22f-b1f1f475c9ee" xlink:to="loc_us-gaap_AccruedBonusesCurrent_01a17848-62f5-7a87-b9bc-59c06b23d409" xlink:type="arc" order="10"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://roivant.com/role/DiscontinuedOperationsNarrativeDetails" xlink:type="simple" xlink:href="roiv-20260930.xsd#DiscontinuedOperationsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://roivant.com/role/DiscontinuedOperationsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_01a1541c-ac02-7364-91c3-b2efe3b3a5e0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019febef-ed28-7cf4-a86f-b4fc7464aca8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_01a1541c-ac02-7364-91c3-b2efe3b3a5e0" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019febef-ed28-7cf4-a86f-b4fc7464aca8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationAxis_01a1541c-ac02-7bc2-82a5-7c880eff10a2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019febef-ed28-7cf4-a86f-b4fc7464aca8" xlink:to="loc_us-gaap_DisposalGroupClassificationAxis_01a1541c-ac02-7bc2-82a5-7c880eff10a2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_01a1541c-ac02-7bc2-82a5-7c880eff10a2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_01a1541c-ac02-7bc2-82a5-7c880eff10a2" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_01a1541c-ac02-7bc2-82a5-7c880eff10a2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_01a1541c-ac02-7ef5-a1de-122898a3e75c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_01a1541c-ac02-7bc2-82a5-7c880eff10a2" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_01a1541c-ac02-7ef5-a1de-122898a3e75c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationsDisposedOfBySaleMember_01a1541c-ac02-7f3f-b5a9-456da93a385a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DiscontinuedOperationsDisposedOfBySaleMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupClassificationDomain_01a1541c-ac02-7ef5-a1de-122898a3e75c" xlink:to="loc_us-gaap_DiscontinuedOperationsDisposedOfBySaleMember_01a1541c-ac02-7f3f-b5a9-456da93a385a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_01a1541c-ac02-7f76-bf83-a1b3489cf848" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019febef-ed28-7cf4-a86f-b4fc7464aca8" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_01a1541c-ac02-7f76-bf83-a1b3489cf848" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_01a1541c-ac02-7f76-bf83-a1b3489cf848_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_01a1541c-ac02-7f76-bf83-a1b3489cf848" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_01a1541c-ac02-7f76-bf83-a1b3489cf848_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_01a1541c-ac02-7563-8c50-06325c65a471" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_01a1541c-ac02-7f76-bf83-a1b3489cf848" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_01a1541c-ac02-7563-8c50-06325c65a471" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_DermavantMember_01a1541c-ac02-79ec-9d89-23d0bcdc652f" xlink:href="roiv-20260930.xsd#roiv_DermavantMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_01a1541c-ac02-7563-8c50-06325c65a471" xlink:to="loc_roiv_DermavantMember_01a1541c-ac02-79ec-9d89-23d0bcdc652f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_DiscontinuedOperationsAmountReceivedFromSaleOfEquityInterest_01a1541c-ac02-7d06-82ae-4c71a4aa1208" xlink:href="roiv-20260930.xsd#roiv_DiscontinuedOperationsAmountReceivedFromSaleOfEquityInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_01a1541c-ac02-7364-91c3-b2efe3b3a5e0" xlink:to="loc_roiv_DiscontinuedOperationsAmountReceivedFromSaleOfEquityInterest_01a1541c-ac02-7d06-82ae-4c71a4aa1208" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_DiscontinuedOperationsAmountReleasedFromEscrow_01a1541c-ac02-7fb3-94dd-fd9c643cf76d" xlink:href="roiv-20260930.xsd#roiv_DiscontinuedOperationsAmountReleasedFromEscrow"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_01a1541c-ac02-7364-91c3-b2efe3b3a5e0" xlink:to="loc_roiv_DiscontinuedOperationsAmountReleasedFromEscrow_01a1541c-ac02-7fb3-94dd-fd9c643cf76d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_DiscontinuedOperationsGainLossFromSaleOfEquityInterest_01a1541c-ac02-7d9a-bcf1-d101f5ee07a3" xlink:href="roiv-20260930.xsd#roiv_DiscontinuedOperationsGainLossFromSaleOfEquityInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_01a1541c-ac02-7364-91c3-b2efe3b3a5e0" xlink:to="loc_roiv_DiscontinuedOperationsGainLossFromSaleOfEquityInterest_01a1541c-ac02-7d9a-bcf1-d101f5ee07a3" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://roivant.com/role/CertainBalanceSheetComponentsNarrativeDetails" xlink:type="simple" xlink:href="roiv-20260930.xsd#CertainBalanceSheetComponentsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://roivant.com/role/CertainBalanceSheetComponentsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_019febef-edc4-73f1-aa87-b72b37d05c39" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable_019febef-edc4-76b5-b395-d99260c30c89" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_019febef-edc4-73f1-aa87-b72b37d05c39" xlink:to="loc_us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable_019febef-edc4-76b5-b395-d99260c30c89" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019febef-edc4-700a-94dd-9db4aee7a4e4" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfResearchAndDevelopmentArrangementContractToPerformForOthersTable_019febef-edc4-76b5-b395-d99260c30c89" xlink:to="loc_dei_LegalEntityAxis_019febef-edc4-700a-94dd-9db4aee7a4e4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019febef-edc4-700a-94dd-9db4aee7a4e4_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019febef-edc4-700a-94dd-9db4aee7a4e4" xlink:to="loc_dei_EntityDomain_019febef-edc4-700a-94dd-9db4aee7a4e4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019febef-edc4-7156-aef7-72999cdfb97d" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019febef-edc4-700a-94dd-9db4aee7a4e4" xlink:to="loc_dei_EntityDomain_019febef-edc4-7156-aef7-72999cdfb97d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_ModernaMember_019febef-edc4-7af1-9350-6cf871f59740" xlink:href="roiv-20260930.xsd#roiv_ModernaMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019febef-edc4-7156-aef7-72999cdfb97d" xlink:to="loc_roiv_ModernaMember_019febef-edc4-7af1-9350-6cf871f59740" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_AccumulatedContractualCosts_019febef-edc4-7f0e-8b89-98f8f44d35c3" xlink:href="roiv-20260930.xsd#roiv_AccumulatedContractualCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_019febef-edc4-73f1-aa87-b72b37d05c39" xlink:to="loc_roiv_AccumulatedContractualCosts_019febef-edc4-7f0e-8b89-98f8f44d35c3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeRelatedLiabilitiesCurrentAndNoncurrent_019febef-edc4-7e9e-a9d0-89208758ff6b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeRelatedLiabilitiesCurrentAndNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_019febef-edc4-73f1-aa87-b72b37d05c39" xlink:to="loc_us-gaap_EmployeeRelatedLiabilitiesCurrentAndNoncurrent_019febef-edc4-7e9e-a9d0-89208758ff6b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpense_019febef-edc4-75ec-a6dc-d6f98de274d7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GeneralAndAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_019febef-edc4-73f1-aa87-b72b37d05c39" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpense_019febef-edc4-75ec-a6dc-d6f98de274d7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpense_019febef-edc4-740b-95d8-1e328685ffb9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ResearchAndDevelopmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersLineItems_019febef-edc4-73f1-aa87-b72b37d05c39" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpense_019febef-edc4-740b-95d8-1e328685ffb9" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://roivant.com/role/ShareholdersEquityDetails" xlink:type="simple" xlink:href="roiv-20260930.xsd#ShareholdersEquityDetails"/>
  <link:definitionLink xlink:role="http://roivant.com/role/ShareholdersEquityDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockLineItems_019febef-edc4-7b7c-80dd-cada5be3c441" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfStockByClassTable_019febef-edc4-73f4-8bbe-90865a597751" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfStockByClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfStockLineItems_019febef-edc4-7b7c-80dd-cada5be3c441" xlink:to="loc_us-gaap_ScheduleOfStockByClassTable_019febef-edc4-73f4-8bbe-90865a597751" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionAxis_019febef-edc4-767e-9ab8-9194e05534b8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_019febef-edc4-73f4-8bbe-90865a597751" xlink:to="loc_us-gaap_RelatedPartyTransactionAxis_019febef-edc4-767e-9ab8-9194e05534b8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_019febef-edc4-767e-9ab8-9194e05534b8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_019febef-edc4-767e-9ab8-9194e05534b8" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_019febef-edc4-767e-9ab8-9194e05534b8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_019febef-edc4-7bf4-9667-98722ebd18ca" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_019febef-edc4-767e-9ab8-9194e05534b8" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_019febef-edc4-7bf4-9667-98722ebd18ca" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_CowenAndCompanyLLCMember_019febef-edc4-7d6c-b960-9638355da189" xlink:href="roiv-20260930.xsd#roiv_CowenAndCompanyLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_019febef-edc4-7bf4-9667-98722ebd18ca" xlink:to="loc_roiv_CowenAndCompanyLLCMember_019febef-edc4-7d6c-b960-9638355da189" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_019febef-edc4-7cf0-a869-377950fac0cf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_019febef-edc4-73f4-8bbe-90865a597751" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_019febef-edc4-7cf0-a869-377950fac0cf" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019febef-edc4-7cf0-a869-377950fac0cf_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_019febef-edc4-7cf0-a869-377950fac0cf" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019febef-edc4-7cf0-a869-377950fac0cf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019febef-edc4-77e5-913e-4621dcf89dda" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_019febef-edc4-7cf0-a869-377950fac0cf" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019febef-edc4-77e5-913e-4621dcf89dda" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_EquityOfferingsAtTheMarketMember_019febef-edc4-7522-8bbd-ec95e96c4bed" xlink:href="roiv-20260930.xsd#roiv_EquityOfferingsAtTheMarketMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_019febef-edc4-77e5-913e-4621dcf89dda" xlink:to="loc_roiv_EquityOfferingsAtTheMarketMember_019febef-edc4-7522-8bbd-ec95e96c4bed" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ShareRepurchaseProgramAxis_019febef-edc4-7f9f-b4d8-6872c78048b7" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ShareRepurchaseProgramAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_019febef-edc4-73f4-8bbe-90865a597751" xlink:to="loc_srt_ShareRepurchaseProgramAxis_019febef-edc4-7f9f-b4d8-6872c78048b7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ShareRepurchaseProgramDomain_019febef-edc4-7f9f-b4d8-6872c78048b7_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ShareRepurchaseProgramDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ShareRepurchaseProgramAxis_019febef-edc4-7f9f-b4d8-6872c78048b7" xlink:to="loc_srt_ShareRepurchaseProgramDomain_019febef-edc4-7f9f-b4d8-6872c78048b7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ShareRepurchaseProgramDomain_019febef-edc4-75e3-a753-b21f3c2129c2" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ShareRepurchaseProgramDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ShareRepurchaseProgramAxis_019febef-edc4-7f9f-b4d8-6872c78048b7" xlink:to="loc_srt_ShareRepurchaseProgramDomain_019febef-edc4-75e3-a753-b21f3c2129c2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_StockRepurchaseProgramMember_019febef-edc4-7b7d-948d-626427800c07" xlink:href="roiv-20260930.xsd#roiv_StockRepurchaseProgramMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ShareRepurchaseProgramDomain_019febef-edc4-75e3-a753-b21f3c2129c2" xlink:to="loc_roiv_StockRepurchaseProgramMember_019febef-edc4-7b7d-948d-626427800c07" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_CommonSharesOfferingPriceAuthorized_019febef-edc4-7ea8-8631-ec6079b35a64" xlink:href="roiv-20260930.xsd#roiv_CommonSharesOfferingPriceAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019febef-edc4-7b7c-80dd-cada5be3c441" xlink:to="loc_roiv_CommonSharesOfferingPriceAuthorized_019febef-edc4-7ea8-8631-ec6079b35a64" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_CommonSharesAggregateOfferingPriceAuthorizedRemainingCapacityAvailable_019febef-edc4-724a-a6bf-0426b74cb1e3" xlink:href="roiv-20260930.xsd#roiv_CommonSharesAggregateOfferingPriceAuthorizedRemainingCapacityAvailable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019febef-edc4-7b7c-80dd-cada5be3c441" xlink:to="loc_roiv_CommonSharesAggregateOfferingPriceAuthorizedRemainingCapacityAvailable_019febef-edc4-724a-a6bf-0426b74cb1e3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StockRepurchaseProgramAuthorizedAmount1_019febef-edc4-7113-84a8-ddc829af9452" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_StockRepurchaseProgramAuthorizedAmount1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019febef-edc4-7b7c-80dd-cada5be3c441" xlink:to="loc_srt_StockRepurchaseProgramAuthorizedAmount1_019febef-edc4-7113-84a8-ddc829af9452" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_ShareRepurchaseProgramIncreasedAuthorizedAmount_019febef-edc4-70be-a8fc-449c56c2ee2a" xlink:href="roiv-20260930.xsd#roiv_ShareRepurchaseProgramIncreasedAuthorizedAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019febef-edc4-7b7c-80dd-cada5be3c441" xlink:to="loc_roiv_ShareRepurchaseProgramIncreasedAuthorizedAmount_019febef-edc4-70be-a8fc-449c56c2ee2a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedDuringPeriodShares_019febef-edc4-79ef-83df-66d99eef886a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockRepurchasedDuringPeriodShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019febef-edc4-7b7c-80dd-cada5be3c441" xlink:to="loc_us-gaap_StockRepurchasedDuringPeriodShares_019febef-edc4-79ef-83df-66d99eef886a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedDuringPeriodValue_019febef-edc4-7268-bc0b-9a7c3484b34d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockRepurchasedDuringPeriodValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019febef-edc4-7b7c-80dd-cada5be3c441" xlink:to="loc_us-gaap_StockRepurchasedDuringPeriodValue_019febef-edc4-7268-bc0b-9a7c3484b34d" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchaseProgramRemainingAuthorizedRepurchaseAmount1_019febef-edc4-7be3-b630-de969fe70bef" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockRepurchaseProgramRemainingAuthorizedRepurchaseAmount1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019febef-edc4-7b7c-80dd-cada5be3c441" xlink:to="loc_us-gaap_StockRepurchaseProgramRemainingAuthorizedRepurchaseAmount1_019febef-edc4-7be3-b630-de969fe70bef" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://roivant.com/role/ShareBasedCompensationNarrativeDetails" xlink:type="simple" xlink:href="roiv-20260930.xsd#ShareBasedCompensationNarrativeDetails"/>
  <link:definitionLink xlink:role="http://roivant.com/role/ShareBasedCompensationNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019febef-edc4-703b-bccc-2ef40d2bbb40" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019febef-edc4-742e-adba-b2ea4d4673f0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019febef-edc4-703b-bccc-2ef40d2bbb40" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019febef-edc4-742e-adba-b2ea4d4673f0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_019febef-edc4-79a2-9f62-3584f9920032" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019febef-edc4-742e-adba-b2ea4d4673f0" xlink:to="loc_us-gaap_PlanNameAxis_019febef-edc4-79a2-9f62-3584f9920032" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019febef-edc4-79a2-9f62-3584f9920032_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_019febef-edc4-79a2-9f62-3584f9920032" xlink:to="loc_us-gaap_PlanNameDomain_019febef-edc4-79a2-9f62-3584f9920032_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019febef-edc4-78ad-82e5-6a3e72a05be6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_019febef-edc4-79a2-9f62-3584f9920032" xlink:to="loc_us-gaap_PlanNameDomain_019febef-edc4-78ad-82e5-6a3e72a05be6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_RoivantSciencesLtd2021EquityIncentivePlanMember_019febef-edc4-70fd-a228-d1cf6b20ed16" xlink:href="roiv-20260930.xsd#roiv_RoivantSciencesLtd2021EquityIncentivePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_019febef-edc4-78ad-82e5-6a3e72a05be6" xlink:to="loc_roiv_RoivantSciencesLtd2021EquityIncentivePlanMember_019febef-edc4-70fd-a228-d1cf6b20ed16" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_SeniorExecutiveCompensationProgramMember_019febef-edc4-7e7e-81ca-55fbdb5267bc" xlink:href="roiv-20260930.xsd#roiv_SeniorExecutiveCompensationProgramMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_019febef-edc4-78ad-82e5-6a3e72a05be6" xlink:to="loc_roiv_SeniorExecutiveCompensationProgramMember_019febef-edc4-7e7e-81ca-55fbdb5267bc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_SubsidiaryEquityIncentivePlansMember_019febef-edc4-7639-9937-c0cf7f462e57" xlink:href="roiv-20260930.xsd#roiv_SubsidiaryEquityIncentivePlansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_019febef-edc4-78ad-82e5-6a3e72a05be6" xlink:to="loc_roiv_SubsidiaryEquityIncentivePlansMember_019febef-edc4-7639-9937-c0cf7f462e57" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019febef-edc4-7cde-81a9-1786fdc8613f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019febef-edc4-742e-adba-b2ea4d4673f0" xlink:to="loc_us-gaap_AwardTypeAxis_019febef-edc4-7cde-81a9-1786fdc8613f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019febef-edc4-7cde-81a9-1786fdc8613f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019febef-edc4-7cde-81a9-1786fdc8613f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019febef-edc4-7cde-81a9-1786fdc8613f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019febef-edc4-71c6-a929-a07b8debd66f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019febef-edc4-7cde-81a9-1786fdc8613f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019febef-edc4-71c6-a929-a07b8debd66f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_019febef-edc4-7a86-8cb0-356d438022d7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019febef-edc4-71c6-a929-a07b8debd66f" xlink:to="loc_us-gaap_PerformanceSharesMember_019febef-edc4-7a86-8cb0-356d438022d7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingAxis_019febef-edc4-7e9a-921e-f47fe7d5d668" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VestingAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019febef-edc4-742e-adba-b2ea4d4673f0" xlink:to="loc_us-gaap_VestingAxis_019febef-edc4-7e9a-921e-f47fe7d5d668" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingDomain_019febef-edc4-7e9a-921e-f47fe7d5d668_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VestingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VestingAxis_019febef-edc4-7e9a-921e-f47fe7d5d668" xlink:to="loc_us-gaap_VestingDomain_019febef-edc4-7e9a-921e-f47fe7d5d668_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingDomain_019febef-edc4-7fa3-9036-15b51f159146" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VestingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VestingAxis_019febef-edc4-7e9a-921e-f47fe7d5d668" xlink:to="loc_us-gaap_VestingDomain_019febef-edc4-7fa3-9036-15b51f159146" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_ShareBasedPaymentArrangementSixthAndFinalTrancheMember_019febef-edc4-701b-8c01-817e276b2aa0" xlink:href="roiv-20260930.xsd#roiv_ShareBasedPaymentArrangementSixthAndFinalTrancheMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_019febef-edc4-7fa3-9036-15b51f159146" xlink:to="loc_roiv_ShareBasedPaymentArrangementSixthAndFinalTrancheMember_019febef-edc4-701b-8c01-817e276b2aa0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_01a1ada1-50f6-7449-8ac2-34b85c6c4ded" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019febef-edc4-742e-adba-b2ea4d4673f0" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_01a1ada1-50f6-7449-8ac2-34b85c6c4ded" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_01a1ada1-50f6-7449-8ac2-34b85c6c4ded_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_01a1ada1-50f6-7449-8ac2-34b85c6c4ded" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_01a1ada1-50f6-7449-8ac2-34b85c6c4ded_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_01a1ada1-50f6-77f7-9461-8e484b28a8a3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_01a1ada1-50f6-7449-8ac2-34b85c6c4ded" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_01a1ada1-50f6-77f7-9461-8e484b28a8a3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_01a1ada1-6dff-7ee7-b99e-5c05c2655d2d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_01a1ada1-50f6-77f7-9461-8e484b28a8a3" xlink:to="loc_us-gaap_SubsequentEventMember_01a1ada1-6dff-7ee7-b99e-5c05c2655d2d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_019febef-edc4-7b08-8a98-de8984017ddc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019febef-edc4-703b-bccc-2ef40d2bbb40" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_019febef-edc4-7b08-8a98-de8984017ddc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_PeriodOfTrailingTradingDaysWeightedAverageTradingPriceUsedToCalculatePerformanceConditionOfPSUs_019febef-edc4-75b1-a384-375e65451b34" xlink:href="roiv-20260930.xsd#roiv_PeriodOfTrailingTradingDaysWeightedAverageTradingPriceUsedToCalculatePerformanceConditionOfPSUs"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019febef-edc4-703b-bccc-2ef40d2bbb40" xlink:to="loc_roiv_PeriodOfTrailingTradingDaysWeightedAverageTradingPriceUsedToCalculatePerformanceConditionOfPSUs_019febef-edc4-75b1-a384-375e65451b34" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharePriceAtTranchePerformancePeriod_019febef-edc4-7404-b22a-084ccf9abc44" xlink:href="roiv-20260930.xsd#roiv_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharePriceAtTranchePerformancePeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019febef-edc4-703b-bccc-2ef40d2bbb40" xlink:to="loc_roiv_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharePriceAtTranchePerformancePeriod_019febef-edc4-7404-b22a-084ccf9abc44" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_NumberOfVestingTranches_019febef-edc4-7003-9565-10975fcd3cd0" xlink:href="roiv-20260930.xsd#roiv_NumberOfVestingTranches"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019febef-edc4-703b-bccc-2ef40d2bbb40" xlink:to="loc_roiv_NumberOfVestingTranches_019febef-edc4-7003-9565-10975fcd3cd0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_PSUsPerformanceConditionSatisfiedShares_019febef-edc4-784e-afdf-f13b5b1d11c6" xlink:href="roiv-20260930.xsd#roiv_PSUsPerformanceConditionSatisfiedShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019febef-edc4-703b-bccc-2ef40d2bbb40" xlink:to="loc_roiv_PSUsPerformanceConditionSatisfiedShares_019febef-edc4-784e-afdf-f13b5b1d11c6" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_PSUsSatisfiedPerformanceConditionShares_019febef-edc4-7e55-b163-1e6f915f065c" xlink:href="roiv-20260930.xsd#roiv_PSUsSatisfiedPerformanceConditionShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019febef-edc4-703b-bccc-2ef40d2bbb40" xlink:to="loc_roiv_PSUsSatisfiedPerformanceConditionShares_019febef-edc4-7e55-b163-1e6f915f065c" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_PSUsHoldingPeriodBeforeCommonSharesMayBeSoldByExecutive_019febef-edc4-7e8f-bcc5-844c0e8cb50f" xlink:href="roiv-20260930.xsd#roiv_PSUsHoldingPeriodBeforeCommonSharesMayBeSoldByExecutive"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019febef-edc4-703b-bccc-2ef40d2bbb40" xlink:to="loc_roiv_PSUsHoldingPeriodBeforeCommonSharesMayBeSoldByExecutive_019febef-edc4-7e8f-bcc5-844c0e8cb50f" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_PSUsWaivedHoldingPeriodBeforeCommonSharesMayBeSoldByExecutive_01a1ada0-88db-77a0-9bfd-58caf09dba36" xlink:href="roiv-20260930.xsd#roiv_PSUsWaivedHoldingPeriodBeforeCommonSharesMayBeSoldByExecutive"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019febef-edc4-703b-bccc-2ef40d2bbb40" xlink:to="loc_roiv_PSUsWaivedHoldingPeriodBeforeCommonSharesMayBeSoldByExecutive_01a1ada0-88db-77a0-9bfd-58caf09dba36" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_019febef-edc4-75f3-9912-518b254eb220" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019febef-edc4-703b-bccc-2ef40d2bbb40" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_019febef-edc4-75f3-9912-518b254eb220" xlink:type="arc" order="8"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://roivant.com/role/ShareBasedCompensationScheduleofActivityforStockOptionsandPerformanceStockOptionsDetails" xlink:type="simple" xlink:href="roiv-20260930.xsd#ShareBasedCompensationScheduleofActivityforStockOptionsandPerformanceStockOptionsDetails"/>
  <link:definitionLink xlink:role="http://roivant.com/role/ShareBasedCompensationScheduleofActivityforStockOptionsandPerformanceStockOptionsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019febef-edc4-7d1f-bcb9-626bdce67d95" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019febef-edc4-77d4-abff-7b337b893249" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019febef-edc4-7d1f-bcb9-626bdce67d95" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019febef-edc4-77d4-abff-7b337b893249" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_019febef-edc4-7485-9182-a57e691d12cb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019febef-edc4-77d4-abff-7b337b893249" xlink:to="loc_us-gaap_PlanNameAxis_019febef-edc4-7485-9182-a57e691d12cb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019febef-edc4-7485-9182-a57e691d12cb_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_019febef-edc4-7485-9182-a57e691d12cb" xlink:to="loc_us-gaap_PlanNameDomain_019febef-edc4-7485-9182-a57e691d12cb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019febef-edc4-702d-96f1-f2f71919347f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_019febef-edc4-7485-9182-a57e691d12cb" xlink:to="loc_us-gaap_PlanNameDomain_019febef-edc4-702d-96f1-f2f71919347f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_RoivantSciencesLtdEquityPlansMember_019febef-edc4-73f8-a074-99089046bc7f" xlink:href="roiv-20260930.xsd#roiv_RoivantSciencesLtdEquityPlansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_019febef-edc4-702d-96f1-f2f71919347f" xlink:to="loc_roiv_RoivantSciencesLtdEquityPlansMember_019febef-edc4-73f8-a074-99089046bc7f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_019febef-edc4-76f5-a3a0-f583aa85bc9f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019febef-edc4-7d1f-bcb9-626bdce67d95" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_019febef-edc4-76f5-a3a0-f583aa85bc9f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_019febef-edc4-7e75-be96-fc0714c5bc9a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_019febef-edc4-76f5-a3a0-f583aa85bc9f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_019febef-edc4-7e75-be96-fc0714c5bc9a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_019febef-edc4-7444-a23f-54ff323076a9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_019febef-edc4-76f5-a3a0-f583aa85bc9f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_019febef-edc4-7444-a23f-54ff323076a9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_019febef-edc4-752a-987f-5b153d28afa8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_019febef-edc4-76f5-a3a0-f583aa85bc9f" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_019febef-edc4-752a-987f-5b153d28afa8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExpirationsInPeriod_01a1785a-5c51-7ef5-befb-99a4e06c4cf1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExpirationsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_019febef-edc4-76f5-a3a0-f583aa85bc9f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExpirationsInPeriod_01a1785a-5c51-7ef5-befb-99a4e06c4cf1" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriod_019febef-edc4-763b-b434-db37fe69cbb6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_019febef-edc4-76f5-a3a0-f583aa85bc9f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriod_019febef-edc4-763b-b434-db37fe69cbb6" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_019febef-edc4-7096-b92e-c582a62678e9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber_019febef-edc4-711d-ac55-f3031aca2ce4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_019febef-edc4-76f5-a3a0-f583aa85bc9f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber_019febef-edc4-711d-ac55-f3031aca2ce4" xlink:type="arc" order="7"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://roivant.com/role/ShareBasedCompensationScheduleofActivityforRSUsandPSUsDetails" xlink:type="simple" xlink:href="roiv-20260930.xsd#ShareBasedCompensationScheduleofActivityforRSUsandPSUsDetails"/>
  <link:definitionLink xlink:role="http://roivant.com/role/ShareBasedCompensationScheduleofActivityforRSUsandPSUsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019febef-edc4-7617-b762-b1085408fbbb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019febef-edc4-752d-bb1a-17993115797f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019febef-edc4-7617-b762-b1085408fbbb" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019febef-edc4-752d-bb1a-17993115797f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019febef-edc4-700d-9c9f-e7a5fb110ad2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019febef-edc4-752d-bb1a-17993115797f" xlink:to="loc_us-gaap_AwardTypeAxis_019febef-edc4-700d-9c9f-e7a5fb110ad2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019febef-edc4-700d-9c9f-e7a5fb110ad2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019febef-edc4-700d-9c9f-e7a5fb110ad2" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019febef-edc4-700d-9c9f-e7a5fb110ad2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019febef-edc4-7604-a0c8-28fa4d883f64" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019febef-edc4-700d-9c9f-e7a5fb110ad2" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019febef-edc4-7604-a0c8-28fa4d883f64" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockMember_019febef-edc4-7f31-a564-7f293700c9da" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019febef-edc4-7604-a0c8-28fa4d883f64" xlink:to="loc_us-gaap_RestrictedStockMember_019febef-edc4-7f31-a564-7f293700c9da" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_019febef-edc4-7bb6-8109-2e11e98df86b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019febef-edc4-7604-a0c8-28fa4d883f64" xlink:to="loc_us-gaap_PerformanceSharesMember_019febef-edc4-7bb6-8109-2e11e98df86b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_019febef-edc4-7ecc-9925-4b5dc1c0ede1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019febef-edc4-752d-bb1a-17993115797f" xlink:to="loc_us-gaap_PlanNameAxis_019febef-edc4-7ecc-9925-4b5dc1c0ede1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019febef-edc4-7ecc-9925-4b5dc1c0ede1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_019febef-edc4-7ecc-9925-4b5dc1c0ede1" xlink:to="loc_us-gaap_PlanNameDomain_019febef-edc4-7ecc-9925-4b5dc1c0ede1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019febef-edc4-7b38-96e3-f56503eaaeb8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_019febef-edc4-7ecc-9925-4b5dc1c0ede1" xlink:to="loc_us-gaap_PlanNameDomain_019febef-edc4-7b38-96e3-f56503eaaeb8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_RoivantSciencesLtdEquityPlansMember_019febef-edc4-7634-9457-0e731b692b74" xlink:href="roiv-20260930.xsd#roiv_RoivantSciencesLtdEquityPlansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_019febef-edc4-7b38-96e3-f56503eaaeb8" xlink:to="loc_roiv_RoivantSciencesLtdEquityPlansMember_019febef-edc4-7634-9457-0e731b692b74" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019febef-edc4-7814-af42-af449825ef78" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019febef-edc4-7617-b762-b1085408fbbb" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019febef-edc4-7814-af42-af449825ef78" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_019febef-edc4-7bdd-8a91-eb68f2bad6e9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019febef-edc4-7814-af42-af449825ef78" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_019febef-edc4-7bdd-8a91-eb68f2bad6e9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019febef-edc4-7706-b241-a272d3374b0e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019febef-edc4-7814-af42-af449825ef78" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019febef-edc4-7706-b241-a272d3374b0e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_019febef-edc4-7882-a61b-73a07d5e5103" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019febef-edc4-7814-af42-af449825ef78" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_019febef-edc4-7882-a61b-73a07d5e5103" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_019febef-edc4-762d-a488-ca77aa886a49" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019febef-edc4-7814-af42-af449825ef78" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_019febef-edc4-762d-a488-ca77aa886a49" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_019febef-edc4-7000-adb3-252d6e03641d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://roivant.com/role/FairValueMeasurementsScheduleofAssetsandLiabilitiesareMeasuredatFairValueonRecurringBasisDetails" xlink:type="simple" xlink:href="roiv-20260930.xsd#FairValueMeasurementsScheduleofAssetsandLiabilitiesareMeasuredatFairValueonRecurringBasisDetails"/>
  <link:definitionLink xlink:role="http://roivant.com/role/FairValueMeasurementsScheduleofAssetsandLiabilitiesareMeasuredatFairValueonRecurringBasisDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019febef-edc4-750a-95a2-197c743b1925" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019febef-edc4-7d68-b9af-035424d7b61d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019febef-edc4-750a-95a2-197c743b1925" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019febef-edc4-7d68-b9af-035424d7b61d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAxis_019febef-edc4-79b3-b480-476d9e2e1c4d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019febef-edc4-7d68-b9af-035424d7b61d" xlink:to="loc_us-gaap_CashAndCashEquivalentsAxis_019febef-edc4-79b3-b480-476d9e2e1c4d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019febef-edc4-79b3-b480-476d9e2e1c4d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CashAndCashEquivalentsAxis_019febef-edc4-79b3-b480-476d9e2e1c4d" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019febef-edc4-79b3-b480-476d9e2e1c4d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019febef-edc4-769e-8fd3-2334cac1df00" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CashAndCashEquivalentsAxis_019febef-edc4-79b3-b480-476d9e2e1c4d" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019febef-edc4-769e-8fd3-2334cac1df00" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MoneyMarketFundsMember_019febef-edc4-7c97-b86b-4d0db922ec42" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MoneyMarketFundsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019febef-edc4-769e-8fd3-2334cac1df00" xlink:to="loc_us-gaap_MoneyMarketFundsMember_019febef-edc4-7c97-b86b-4d0db922ec42" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019febef-edc4-7b72-b188-8fee5dd39be3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019febef-edc4-7d68-b9af-035424d7b61d" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019febef-edc4-7b72-b188-8fee5dd39be3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019febef-edc4-7b72-b188-8fee5dd39be3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019febef-edc4-7b72-b188-8fee5dd39be3" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019febef-edc4-7b72-b188-8fee5dd39be3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019febef-edc4-754b-9080-d8350fd022b4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019febef-edc4-7b72-b188-8fee5dd39be3" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019febef-edc4-754b-9080-d8350fd022b4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_019febef-edc4-7448-94c5-ea7255f6d0eb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019febef-edc4-754b-9080-d8350fd022b4" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_019febef-edc4-7448-94c5-ea7255f6d0eb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_019febef-edc4-738a-b7e4-e730d8822983" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019febef-edc4-754b-9080-d8350fd022b4" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_019febef-edc4-738a-b7e4-e730d8822983" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_019febef-edc4-74b1-a101-0c87e7959645" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019febef-edc4-754b-9080-d8350fd022b4" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_019febef-edc4-74b1-a101-0c87e7959645" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019febef-edc4-7b42-b9a0-4b39fb72a48f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019febef-edc4-7d68-b9af-035424d7b61d" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019febef-edc4-7b42-b9a0-4b39fb72a48f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019febef-edc4-7b42-b9a0-4b39fb72a48f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019febef-edc4-7b42-b9a0-4b39fb72a48f" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019febef-edc4-7b42-b9a0-4b39fb72a48f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019febef-edc4-74de-849b-5107cc05d775" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019febef-edc4-7b42-b9a0-4b39fb72a48f" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019febef-edc4-74de-849b-5107cc05d775" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USTreasurySecuritiesMember_019febef-edc4-7217-bf1e-c0109b6f0a89" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_USTreasurySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019febef-edc4-74de-849b-5107cc05d775" xlink:to="loc_us-gaap_USTreasurySecuritiesMember_019febef-edc4-7217-bf1e-c0109b6f0a89" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateBondSecuritiesMember_019febef-edc4-7f72-b6ed-1260d6237f9d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CorporateBondSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019febef-edc4-74de-849b-5107cc05d775" xlink:to="loc_us-gaap_CorporateBondSecuritiesMember_019febef-edc4-7f72-b6ed-1260d6237f9d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialPaperMember_01a1785e-824f-73b9-be51-77c325c2d8b0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommercialPaperMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019febef-edc4-74de-849b-5107cc05d775" xlink:to="loc_us-gaap_CommercialPaperMember_01a1785e-824f-73b9-be51-77c325c2d8b0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019febef-edc4-728e-8ede-c117daaab44f" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019febef-edc4-7d68-b9af-035424d7b61d" xlink:to="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019febef-edc4-728e-8ede-c117daaab44f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_019febef-edc4-728e-8ede-c117daaab44f_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019febef-edc4-728e-8ede-c117daaab44f" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_019febef-edc4-728e-8ede-c117daaab44f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_019febef-edc4-772a-8c02-d0bc982b0bb2" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019febef-edc4-728e-8ede-c117daaab44f" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_019febef-edc4-772a-8c02-d0bc982b0bb2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_DatavantHoldingsIncMember_019febef-edc4-723f-833a-93545c1daf59" xlink:href="roiv-20260930.xsd#roiv_DatavantHoldingsIncMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_019febef-edc4-772a-8c02-d0bc982b0bb2" xlink:to="loc_roiv_DatavantHoldingsIncMember_019febef-edc4-723f-833a-93545c1daf59" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_ArbutusBiopharmaCorporationMember_019febef-edc4-79df-a4f8-ee6492f95c5e" xlink:href="roiv-20260930.xsd#roiv_ArbutusBiopharmaCorporationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_019febef-edc4-772a-8c02-d0bc982b0bb2" xlink:to="loc_roiv_ArbutusBiopharmaCorporationMember_019febef-edc4-79df-a4f8-ee6492f95c5e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByAssetClassAxis_019febef-edc4-7429-a80b-9c4d86e7f98b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByAssetClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019febef-edc4-7d68-b9af-035424d7b61d" xlink:to="loc_us-gaap_FairValueByAssetClassAxis_019febef-edc4-7429-a80b-9c4d86e7f98b" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019febef-edc4-7429-a80b-9c4d86e7f98b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_019febef-edc4-7429-a80b-9c4d86e7f98b" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019febef-edc4-7429-a80b-9c4d86e7f98b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019febef-edc4-7b27-be4e-b55f1d87705f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_019febef-edc4-7429-a80b-9c4d86e7f98b" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019febef-edc4-7b27-be4e-b55f1d87705f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019febef-edc4-7729-a235-5845865bca6b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_019febef-edc4-7b27-be4e-b55f1d87705f" xlink:to="loc_us-gaap_CommonStockMember_019febef-edc4-7729-a235-5845865bca6b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosureAbstract_019febef-edc4-7610-87b5-ad954a363cf1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsFairValueDisclosureAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019febef-edc4-750a-95a2-197c743b1925" xlink:to="loc_us-gaap_AssetsFairValueDisclosureAbstract_019febef-edc4-7610-87b5-ad954a363cf1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_019febef-edc4-70d3-8157-cf2e7f4d5b8a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_019febef-edc4-7610-87b5-ad954a363cf1" xlink:to="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_019febef-edc4-70d3-8157-cf2e7f4d5b8a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest_019febef-edc4-7a92-9f91-01c609fe6ccd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_019febef-edc4-7610-87b5-ad954a363cf1" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest_019febef-edc4-7a92-9f91-01c609fe6ccd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentsFairValueDisclosure_019febef-edc4-7d6d-aaa8-40cf35a29e0e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_019febef-edc4-7610-87b5-ad954a363cf1" xlink:to="loc_us-gaap_InvestmentsFairValueDisclosure_019febef-edc4-7d6d-aaa8-40cf35a29e0e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosure_019febef-edc4-74c5-89b3-768cfb9c7c16" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_019febef-edc4-7610-87b5-ad954a363cf1" xlink:to="loc_us-gaap_AssetsFairValueDisclosure_019febef-edc4-74c5-89b3-768cfb9c7c16" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://roivant.com/role/FairValueMeasurementsNarrativeDetails" xlink:type="simple" xlink:href="roiv-20260930.xsd#FairValueMeasurementsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://roivant.com/role/FairValueMeasurementsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019febef-edc4-7f3d-89ed-d2cd5f9b697a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019febef-edc4-7595-a53b-705307354bbf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019febef-edc4-7f3d-89ed-d2cd5f9b697a" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019febef-edc4-7595-a53b-705307354bbf" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019febef-edc4-7ea3-8018-b38260446ee1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_019febef-edc4-7595-a53b-705307354bbf" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019febef-edc4-7ea3-8018-b38260446ee1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019febef-edc4-7ea3-8018-b38260446ee1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019febef-edc4-7ea3-8018-b38260446ee1" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019febef-edc4-7ea3-8018-b38260446ee1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019febef-edc4-7dab-98f2-b80d112782e9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019febef-edc4-7ea3-8018-b38260446ee1" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019febef-edc4-7dab-98f2-b80d112782e9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_019febef-edc4-7dad-b486-7a6b9350eb06" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019febef-edc4-7dab-98f2-b80d112782e9" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_019febef-edc4-7dad-b486-7a6b9350eb06" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesFairValueDisclosure_019febef-edc4-7511-b909-30ad74a9e299" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019febef-edc4-7f3d-89ed-d2cd5f9b697a" xlink:to="loc_us-gaap_LiabilitiesFairValueDisclosure_019febef-edc4-7511-b909-30ad74a9e299" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityTransfersNet_019febef-edc4-78ca-8cd3-1ee522adfecd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityTransfersNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_019febef-edc4-7f3d-89ed-d2cd5f9b697a" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityTransfersNet_019febef-edc4-78ca-8cd3-1ee522adfecd" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://roivant.com/role/FairValueMeasurementsScheduleofChangesinFairValueoftheLevel3AssetsDetails" xlink:type="simple" xlink:href="roiv-20260930.xsd#FairValueMeasurementsScheduleofChangesinFairValueoftheLevel3AssetsDetails"/>
  <link:definitionLink xlink:role="http://roivant.com/role/FairValueMeasurementsScheduleofChangesinFairValueoftheLevel3AssetsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019febef-edc4-7df5-9296-0e0519f49938" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019febef-edc4-7af6-8b19-f41862913b18" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019febef-edc4-7df5-9296-0e0519f49938" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019febef-edc4-7af6-8b19-f41862913b18" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019febef-edc4-79ae-b27b-65e5ea49af47" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019febef-edc4-7af6-8b19-f41862913b18" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019febef-edc4-79ae-b27b-65e5ea49af47" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019febef-edc4-79ae-b27b-65e5ea49af47_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019febef-edc4-79ae-b27b-65e5ea49af47" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019febef-edc4-79ae-b27b-65e5ea49af47_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019febef-edc4-7848-a162-4e85cba771e0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019febef-edc4-79ae-b27b-65e5ea49af47" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019febef-edc4-7848-a162-4e85cba771e0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_019febef-edc4-7dc8-b9ae-58a54392788e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019febef-edc4-7848-a162-4e85cba771e0" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_019febef-edc4-7dc8-b9ae-58a54392788e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019febef-edc4-7585-97df-e736424505eb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019febef-edc4-7df5-9296-0e0519f49938" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019febef-edc4-7585-97df-e736424505eb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue_019febef-edc4-71f6-8b22-02c54e11da0b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019febef-edc4-7585-97df-e736424505eb" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue_019febef-edc4-71f6-8b22-02c54e11da0b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1_019febef-edc4-7e18-b470-58fc0b361729" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019febef-edc4-7585-97df-e736424505eb" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1_019febef-edc4-7e18-b470-58fc0b361729" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue_019febef-edc4-76c5-8321-6914d751dc40" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueRecurringBasisUnobservableInputReconciliationAssetGainLossStatementOfIncomeExtensibleList_019febef-edc4-7ae9-b2a4-2c34a67f7ec8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueRecurringBasisUnobservableInputReconciliationAssetGainLossStatementOfIncomeExtensibleList"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019febef-edc4-7df5-9296-0e0519f49938" xlink:to="loc_us-gaap_FairValueRecurringBasisUnobservableInputReconciliationAssetGainLossStatementOfIncomeExtensibleList_019febef-edc4-7ae9-b2a4-2c34a67f7ec8" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://roivant.com/role/FairValueMeasurementsScheduleofChangesinFairValueoftheLevel3LiabilitiesDetails" xlink:type="simple" xlink:href="roiv-20260930.xsd#FairValueMeasurementsScheduleofChangesinFairValueoftheLevel3LiabilitiesDetails"/>
  <link:definitionLink xlink:role="http://roivant.com/role/FairValueMeasurementsScheduleofChangesinFairValueoftheLevel3LiabilitiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019febef-edc4-74d0-8408-023e2afbd249" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019febef-edc4-7388-bb2d-ef483555dd53" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019febef-edc4-74d0-8408-023e2afbd249" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019febef-edc4-7388-bb2d-ef483555dd53" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019febef-edc4-7c63-a84d-f15493b02a29" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019febef-edc4-7388-bb2d-ef483555dd53" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019febef-edc4-7c63-a84d-f15493b02a29" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019febef-edc4-7c63-a84d-f15493b02a29_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019febef-edc4-7c63-a84d-f15493b02a29" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019febef-edc4-7c63-a84d-f15493b02a29_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019febef-edc4-745d-bc07-6ceefbb522ae" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019febef-edc4-7c63-a84d-f15493b02a29" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019febef-edc4-745d-bc07-6ceefbb522ae" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_019febef-edc4-78f7-9a95-75d63706ce8a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019febef-edc4-745d-bc07-6ceefbb522ae" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_019febef-edc4-78f7-9a95-75d63706ce8a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019febef-edc4-7247-a7a5-dbfd78782747" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019febef-edc4-74d0-8408-023e2afbd249" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019febef-edc4-7247-a7a5-dbfd78782747" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_019febef-edc4-7ff3-a5e5-1adfef757c15" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019febef-edc4-7247-a7a5-dbfd78782747" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_019febef-edc4-7ff3-a5e5-1adfef757c15" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings_019febef-edc4-7e09-9885-9e13acc0cfb0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019febef-edc4-7247-a7a5-dbfd78782747" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings_019febef-edc4-7e09-9885-9e13acc0cfb0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_019febef-edc4-7050-8872-ceef5dee3ed1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueRecurringBasisUnobservableInputReconciliationLiabilityGainLossStatementOfIncomeExtensibleList_019febef-edc4-70fb-b52d-7e2491c273fb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueRecurringBasisUnobservableInputReconciliationLiabilityGainLossStatementOfIncomeExtensibleList"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019febef-edc4-74d0-8408-023e2afbd249" xlink:to="loc_us-gaap_FairValueRecurringBasisUnobservableInputReconciliationLiabilityGainLossStatementOfIncomeExtensibleList_019febef-edc4-70fb-b52d-7e2491c273fb" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://roivant.com/role/FairValueMeasurementsScheduleofInvestmentinDatavantDetails" xlink:type="simple" xlink:href="roiv-20260930.xsd#FairValueMeasurementsScheduleofInvestmentinDatavantDetails"/>
  <link:definitionLink xlink:role="http://roivant.com/role/FairValueMeasurementsScheduleofInvestmentinDatavantDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_019febef-edc4-71c0-aab0-80b857cb588c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_019febef-edc4-7124-9dc1-5c04dad358ea" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_019febef-edc4-71c0-aab0-80b857cb588c" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_019febef-edc4-7124-9dc1-5c04dad358ea" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019febef-edc4-77ed-83a9-07cee62f5266" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_019febef-edc4-7124-9dc1-5c04dad358ea" xlink:to="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019febef-edc4-77ed-83a9-07cee62f5266" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_019febef-edc4-77ed-83a9-07cee62f5266_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019febef-edc4-77ed-83a9-07cee62f5266" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_019febef-edc4-77ed-83a9-07cee62f5266_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_019febef-edc4-78b3-9cab-2b0e17cbcab0" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019febef-edc4-77ed-83a9-07cee62f5266" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_019febef-edc4-78b3-9cab-2b0e17cbcab0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_DatavantHoldingsIncMember_019febef-edc4-70e7-b30e-7d0e3e2b75c7" xlink:href="roiv-20260930.xsd#roiv_DatavantHoldingsIncMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_019febef-edc4-78b3-9cab-2b0e17cbcab0" xlink:to="loc_roiv_DatavantHoldingsIncMember_019febef-edc4-70e7-b30e-7d0e3e2b75c7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeAxis_019febef-edc4-7c8d-b7d0-c7f0aa52a1bc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_019febef-edc4-7124-9dc1-5c04dad358ea" xlink:to="loc_us-gaap_MeasurementInputTypeAxis_019febef-edc4-7c8d-b7d0-c7f0aa52a1bc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_019febef-edc4-7c8d-b7d0-c7f0aa52a1bc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_MeasurementInputTypeAxis_019febef-edc4-7c8d-b7d0-c7f0aa52a1bc" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_019febef-edc4-7c8d-b7d0-c7f0aa52a1bc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_019febef-edc4-7f44-8955-a2b1952b20ec" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_MeasurementInputTypeAxis_019febef-edc4-7c8d-b7d0-c7f0aa52a1bc" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_019febef-edc4-7f44-8955-a2b1952b20ec" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputPriceVolatilityMember_019febef-edc4-73e5-9d65-a46e1ae64b7e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputPriceVolatilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_019febef-edc4-7f44-8955-a2b1952b20ec" xlink:to="loc_us-gaap_MeasurementInputPriceVolatilityMember_019febef-edc4-73e5-9d65-a46e1ae64b7e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputDiscountRateMember_019febef-edc4-71ed-a635-1c28f1af0139" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputDiscountRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_019febef-edc4-7f44-8955-a2b1952b20ec" xlink:to="loc_us-gaap_MeasurementInputDiscountRateMember_019febef-edc4-71ed-a635-1c28f1af0139" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_FairValueAssetMeasurementInput_019febef-edc4-75a6-81f5-1ab8586dc8eb" xlink:href="roiv-20260930.xsd#roiv_FairValueAssetMeasurementInput"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_019febef-edc4-71c0-aab0-80b857cb588c" xlink:to="loc_roiv_FairValueAssetMeasurementInput_019febef-edc4-75a6-81f5-1ab8586dc8eb" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://roivant.com/role/NetLossperCommonShareScheduleofPotentiallyDilutiveCommonStockEquivalentsExcludedfromComputationofDilutedNetLossperCommonShareDetails" xlink:type="simple" xlink:href="roiv-20260930.xsd#NetLossperCommonShareScheduleofPotentiallyDilutiveCommonStockEquivalentsExcludedfromComputationofDilutedNetLossperCommonShareDetails"/>
  <link:definitionLink xlink:role="http://roivant.com/role/NetLossperCommonShareScheduleofPotentiallyDilutiveCommonStockEquivalentsExcludedfromComputationofDilutedNetLossperCommonShareDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_019febef-edc4-7494-9813-1e8b7ac8aed1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_019febef-edc4-7b03-8bc9-320b99991358" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_019febef-edc4-7494-9813-1e8b7ac8aed1" xlink:to="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_019febef-edc4-7b03-8bc9-320b99991358" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019febef-edc4-70b5-a751-e61408e50948" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_019febef-edc4-7b03-8bc9-320b99991358" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019febef-edc4-70b5-a751-e61408e50948" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019febef-edc4-70b5-a751-e61408e50948_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019febef-edc4-70b5-a751-e61408e50948" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019febef-edc4-70b5-a751-e61408e50948_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019febef-edc4-7c84-820e-8c3dc8900c97" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019febef-edc4-70b5-a751-e61408e50948" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019febef-edc4-7c84-820e-8c3dc8900c97" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_StockOptionsAndPerformanceStockOptionsMember_019febef-edc4-7b89-bfef-dc4baffd4836" xlink:href="roiv-20260930.xsd#roiv_StockOptionsAndPerformanceStockOptionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019febef-edc4-7c84-820e-8c3dc8900c97" xlink:to="loc_roiv_StockOptionsAndPerformanceStockOptionsMember_019febef-edc4-7b89-bfef-dc4baffd4836" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_RestrictedStockAndPerformanceStockUnitsMember_019febef-edc4-7557-a620-702870d9756f" xlink:href="roiv-20260930.xsd#roiv_RestrictedStockAndPerformanceStockUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019febef-edc4-7c84-820e-8c3dc8900c97" xlink:to="loc_roiv_RestrictedStockAndPerformanceStockUnitsMember_019febef-edc4-7557-a620-702870d9756f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_March2020CappedValueAppreciationRightsGrantsMember_019febef-edc4-7e29-95b1-ad84488cc0d8" xlink:href="roiv-20260930.xsd#roiv_March2020CappedValueAppreciationRightsGrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019febef-edc4-7c84-820e-8c3dc8900c97" xlink:to="loc_roiv_March2020CappedValueAppreciationRightsGrantsMember_019febef-edc4-7e29-95b1-ad84488cc0d8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_EarnOutSharesNonvestedMember_019febef-edc4-780a-8124-b1eb53de806d" xlink:href="roiv-20260930.xsd#roiv_EarnOutSharesNonvestedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019febef-edc4-7c84-820e-8c3dc8900c97" xlink:to="loc_roiv_EarnOutSharesNonvestedMember_019febef-edc4-780a-8124-b1eb53de806d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_OtherStockBasedAwardsAndInstrumentsIssuedMember_019febef-edc4-7135-9f35-8e5d7406aec5" xlink:href="roiv-20260930.xsd#roiv_OtherStockBasedAwardsAndInstrumentsIssuedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019febef-edc4-7c84-820e-8c3dc8900c97" xlink:to="loc_roiv_OtherStockBasedAwardsAndInstrumentsIssuedMember_019febef-edc4-7135-9f35-8e5d7406aec5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_019febef-edc4-7b49-bcfb-a7f7594a6989" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_019febef-edc4-7494-9813-1e8b7ac8aed1" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_019febef-edc4-7b49-bcfb-a7f7594a6989" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://roivant.com/role/SegmentInformationScheduleofSignificantSegmentExpensesDetails" xlink:type="simple" xlink:href="roiv-20260930.xsd#SegmentInformationScheduleofSignificantSegmentExpensesDetails"/>
  <link:definitionLink xlink:role="http://roivant.com/role/SegmentInformationScheduleofSignificantSegmentExpensesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_019febef-edc4-7b11-ae95-87ea83eb0b19" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019febef-edc4-7b9b-a01b-8b9b2ba9ceb3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019febef-edc4-7b11-ae95-87ea83eb0b19" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019febef-edc4-7b9b-a01b-8b9b2ba9ceb3" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019febef-edc4-74eb-bf24-d4e4fa148f56" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementOfIncomeLocationBalanceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019febef-edc4-7b9b-a01b-8b9b2ba9ceb3" xlink:to="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_019febef-edc4-74eb-bf24-d4e4fa148f56" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019febef-edc4-7b24-8334-c12b19d42519" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019febef-edc4-7b9b-a01b-8b9b2ba9ceb3" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019febef-edc4-7b24-8334-c12b19d42519" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019febef-edc4-7b24-8334-c12b19d42519_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019febef-edc4-7b24-8334-c12b19d42519" xlink:to="loc_us-gaap_SegmentDomain_019febef-edc4-7b24-8334-c12b19d42519_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019febef-edc4-767d-a848-ae36bba2789e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019febef-edc4-7b24-8334-c12b19d42519" xlink:to="loc_us-gaap_SegmentDomain_019febef-edc4-767d-a848-ae36bba2789e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_ReportableSegmentMember_019febef-edc4-73df-bc3e-e8b267869db4" xlink:href="roiv-20260930.xsd#roiv_ReportableSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019febef-edc4-767d-a848-ae36bba2789e" xlink:to="loc_roiv_ReportableSegmentMember_019febef-edc4-73df-bc3e-e8b267869db4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019febef-edc4-7ce6-bb8b-2d82694c48ca" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019febef-edc4-7b9b-a01b-8b9b2ba9ceb3" xlink:to="loc_srt_ProductOrServiceAxis_019febef-edc4-7ce6-bb8b-2d82694c48ca" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019febef-edc4-7ce6-bb8b-2d82694c48ca_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_019febef-edc4-7ce6-bb8b-2d82694c48ca" xlink:to="loc_srt_ProductsAndServicesDomain_019febef-edc4-7ce6-bb8b-2d82694c48ca_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019febef-edc4-7818-87f9-60fa0737b099" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_019febef-edc4-7ce6-bb8b-2d82694c48ca" xlink:to="loc_srt_ProductsAndServicesDomain_019febef-edc4-7818-87f9-60fa0737b099" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductMember_01a15424-d614-7970-929d-271035410922" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProductMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019febef-edc4-7818-87f9-60fa0737b099" xlink:to="loc_us-gaap_ProductMember_01a15424-d614-7970-929d-271035410922" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_LicenseMilestoneAndOtherRevenueMember_01a15425-1dd3-7c0a-9fbb-f6b7e2ff0b42" xlink:href="roiv-20260930.xsd#roiv_LicenseMilestoneAndOtherRevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019febef-edc4-7818-87f9-60fa0737b099" xlink:to="loc_roiv_LicenseMilestoneAndOtherRevenueMember_01a15425-1dd3-7c0a-9fbb-f6b7e2ff0b42" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_AntiFcRnFranchiseEndocrineDiseasesMember_019febef-edc4-73b0-96af-e028b6d7cf2a" xlink:href="roiv-20260930.xsd#roiv_AntiFcRnFranchiseEndocrineDiseasesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019febef-edc4-7818-87f9-60fa0737b099" xlink:to="loc_roiv_AntiFcRnFranchiseEndocrineDiseasesMember_019febef-edc4-73b0-96af-e028b6d7cf2a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_AntiFcRnFranchiseNeurologicalDiseasesMember_019febef-edc4-7d0d-a5a7-c8593a991255" xlink:href="roiv-20260930.xsd#roiv_AntiFcRnFranchiseNeurologicalDiseasesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019febef-edc4-7818-87f9-60fa0737b099" xlink:to="loc_roiv_AntiFcRnFranchiseNeurologicalDiseasesMember_019febef-edc4-7d0d-a5a7-c8593a991255" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_AntiFcRnFranchiseRheumatologyDiseasesMember_019febef-edc4-76fc-9c68-c899486ab9e1" xlink:href="roiv-20260930.xsd#roiv_AntiFcRnFranchiseRheumatologyDiseasesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019febef-edc4-7818-87f9-60fa0737b099" xlink:to="loc_roiv_AntiFcRnFranchiseRheumatologyDiseasesMember_019febef-edc4-76fc-9c68-c899486ab9e1" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_AntiFcRnFranchiseDermatologyDiseasesMember_019febef-edc4-74cd-856e-09d3df653f6b" xlink:href="roiv-20260930.xsd#roiv_AntiFcRnFranchiseDermatologyDiseasesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019febef-edc4-7818-87f9-60fa0737b099" xlink:to="loc_roiv_AntiFcRnFranchiseDermatologyDiseasesMember_019febef-edc4-74cd-856e-09d3df653f6b" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_AntiFcRnFranchiseOtherClinicalAndNonclinicalMember_019febef-edc4-79b1-9977-644672365203" xlink:href="roiv-20260930.xsd#roiv_AntiFcRnFranchiseOtherClinicalAndNonclinicalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019febef-edc4-7818-87f9-60fa0737b099" xlink:to="loc_roiv_AntiFcRnFranchiseOtherClinicalAndNonclinicalMember_019febef-edc4-79b1-9977-644672365203" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_BrepocitinibMember_019febef-edc4-70bb-88e3-8bfdda20f1e2" xlink:href="roiv-20260930.xsd#roiv_BrepocitinibMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019febef-edc4-7818-87f9-60fa0737b099" xlink:to="loc_roiv_BrepocitinibMember_019febef-edc4-70bb-88e3-8bfdda20f1e2" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_MosliciguatMember_019febef-edc4-7e05-bb55-b7a7ed95253d" xlink:href="roiv-20260930.xsd#roiv_MosliciguatMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019febef-edc4-7818-87f9-60fa0737b099" xlink:to="loc_roiv_MosliciguatMember_019febef-edc4-7e05-bb55-b7a7ed95253d" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_OtherDevelopmentAndDiscoveryProgramsMember_019febef-edc4-76f6-945a-cf68828982d2" xlink:href="roiv-20260930.xsd#roiv_OtherDevelopmentAndDiscoveryProgramsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019febef-edc4-7818-87f9-60fa0737b099" xlink:to="loc_roiv_OtherDevelopmentAndDiscoveryProgramsMember_019febef-edc4-76f6-945a-cf68828982d2" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019febef-edc4-7a38-8692-4cfc3643d7c5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019febef-edc4-7b11-ae95-87ea83eb0b19" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019febef-edc4-7a38-8692-4cfc3643d7c5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingExpensesAbstract_019febef-edc4-7df5-a7a4-b5e3d0446164" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingExpensesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019febef-edc4-7b11-ae95-87ea83eb0b19" xlink:to="loc_us-gaap_OperatingExpensesAbstract_019febef-edc4-7df5-a7a4-b5e3d0446164" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfRevenue_019febef-edc4-7d5d-9171-770909dbb4b9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostOfRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019febef-edc4-7df5-a7a4-b5e3d0446164" xlink:to="loc_us-gaap_CostOfRevenue_019febef-edc4-7d5d-9171-770909dbb4b9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpense_019febef-edc4-7a9c-9fff-938eee4bd88b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ResearchAndDevelopmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019febef-edc4-7df5-a7a4-b5e3d0446164" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpense_019febef-edc4-7a9c-9fff-938eee4bd88b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherResearchAndDevelopmentExpense_019febef-edc4-769f-80c3-5ff6622b596a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherResearchAndDevelopmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019febef-edc4-7df5-a7a4-b5e3d0446164" xlink:to="loc_us-gaap_OtherResearchAndDevelopmentExpense_019febef-edc4-769f-80c3-5ff6622b596a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensation_019febef-edc4-73b4-b81c-3e264225e481" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019febef-edc4-7df5-a7a4-b5e3d0446164" xlink:to="loc_us-gaap_ShareBasedCompensation_019febef-edc4-73b4-b81c-3e264225e481" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_PersonnelRelatedExpenses_019febef-edc4-7717-b4cf-6083a8476949" xlink:href="roiv-20260930.xsd#roiv_PersonnelRelatedExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019febef-edc4-7df5-a7a4-b5e3d0446164" xlink:to="loc_roiv_PersonnelRelatedExpenses_019febef-edc4-7717-b4cf-6083a8476949" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherGeneralAndAdministrativeExpense_019febef-edc4-7f83-bbf3-23b9f3704cbd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherGeneralAndAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019febef-edc4-7df5-a7a4-b5e3d0446164" xlink:to="loc_us-gaap_OtherGeneralAndAdministrativeExpense_019febef-edc4-7f83-bbf3-23b9f3704cbd" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LitigationSettlementGain_019febef-edc4-7a45-b70e-fde8f9dbebb9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LitigationSettlementGain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019febef-edc4-7df5-a7a4-b5e3d0446164" xlink:to="loc_us-gaap_LitigationSettlementGain_019febef-edc4-7a45-b70e-fde8f9dbebb9" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnInvestments_019febef-edc4-773b-ad3e-4c09560966e8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainLossOnInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019febef-edc4-7df5-a7a4-b5e3d0446164" xlink:to="loc_us-gaap_GainLossOnInvestments_019febef-edc4-773b-ad3e-4c09560966e8" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_GainLossOnFairValueOfLiabilityInstruments_019febef-edc4-730c-adec-768598f7cf55" xlink:href="roiv-20260930.xsd#roiv_GainLossOnFairValueOfLiabilityInstruments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019febef-edc4-7df5-a7a4-b5e3d0446164" xlink:to="loc_roiv_GainLossOnFairValueOfLiabilityInstruments_019febef-edc4-730c-adec-768598f7cf55" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentIncomeInterest_019febef-edc4-7b51-aea1-2ead99e9437e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentIncomeInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019febef-edc4-7df5-a7a4-b5e3d0446164" xlink:to="loc_us-gaap_InvestmentIncomeInterest_019febef-edc4-7b51-aea1-2ead99e9437e" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_019febef-edc4-71dd-a88e-82c91cee9392" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherNonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019febef-edc4-7df5-a7a4-b5e3d0446164" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_019febef-edc4-71dd-a88e-82c91cee9392" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_019febef-edc4-7b49-a901-527518db1cb2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019febef-edc4-7df5-a7a4-b5e3d0446164" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_019febef-edc4-7b49-a901-527518db1cb2" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTax_01a15420-f025-7064-9df7-1af905df741f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019febef-edc4-7df5-a7a4-b5e3d0446164" xlink:to="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTax_01a15420-f025-7064-9df7-1af905df741f" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_019febef-edc4-781a-ab04-c278ecab40b1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019febef-edc4-7df5-a7a4-b5e3d0446164" xlink:to="loc_us-gaap_ProfitLoss_019febef-edc4-781a-ab04-c278ecab40b1" xlink:type="arc" order="14"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://roivant.com/role/SegmentInformationScheduleofSignificantSegmentExpensesDetails_1" xlink:type="simple" xlink:href="roiv-20260930.xsd#SegmentInformationScheduleofSignificantSegmentExpensesDetails_1"/>
  <link:definitionLink xlink:role="http://roivant.com/role/SegmentInformationScheduleofSignificantSegmentExpensesDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_019febef-edc4-7b11-ae95-87ea83eb0b19" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019febef-edc4-7b9b-a01b-8b9b2ba9ceb3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019febef-edc4-7b11-ae95-87ea83eb0b19" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019febef-edc4-7b9b-a01b-8b9b2ba9ceb3" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019febef-edc4-7b24-8334-c12b19d42519" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019febef-edc4-7b9b-a01b-8b9b2ba9ceb3" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019febef-edc4-7b24-8334-c12b19d42519" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019febef-edc4-7b24-8334-c12b19d42519_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019febef-edc4-7b24-8334-c12b19d42519" xlink:to="loc_us-gaap_SegmentDomain_019febef-edc4-7b24-8334-c12b19d42519_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019febef-edc4-767d-a848-ae36bba2789e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019febef-edc4-7b24-8334-c12b19d42519" xlink:to="loc_us-gaap_SegmentDomain_019febef-edc4-767d-a848-ae36bba2789e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_ReportableSegmentMember_019febef-edc4-73df-bc3e-e8b267869db4" xlink:href="roiv-20260930.xsd#roiv_ReportableSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019febef-edc4-767d-a848-ae36bba2789e" xlink:to="loc_roiv_ReportableSegmentMember_019febef-edc4-73df-bc3e-e8b267869db4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019febef-edc4-7ce6-bb8b-2d82694c48ca" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019febef-edc4-7b9b-a01b-8b9b2ba9ceb3" xlink:to="loc_srt_ProductOrServiceAxis_019febef-edc4-7ce6-bb8b-2d82694c48ca" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019febef-edc4-7ce6-bb8b-2d82694c48ca_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_019febef-edc4-7ce6-bb8b-2d82694c48ca" xlink:to="loc_srt_ProductsAndServicesDomain_019febef-edc4-7ce6-bb8b-2d82694c48ca_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019febef-edc4-7818-87f9-60fa0737b099" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_019febef-edc4-7ce6-bb8b-2d82694c48ca" xlink:to="loc_srt_ProductsAndServicesDomain_019febef-edc4-7818-87f9-60fa0737b099" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductMember_01a15424-d614-7970-929d-271035410922" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProductMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019febef-edc4-7818-87f9-60fa0737b099" xlink:to="loc_us-gaap_ProductMember_01a15424-d614-7970-929d-271035410922" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_LicenseMilestoneAndOtherRevenueMember_01a15425-1dd3-7c0a-9fbb-f6b7e2ff0b42" xlink:href="roiv-20260930.xsd#roiv_LicenseMilestoneAndOtherRevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019febef-edc4-7818-87f9-60fa0737b099" xlink:to="loc_roiv_LicenseMilestoneAndOtherRevenueMember_01a15425-1dd3-7c0a-9fbb-f6b7e2ff0b42" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_AntiFcRnFranchiseEndocrineDiseasesMember_019febef-edc4-73b0-96af-e028b6d7cf2a" xlink:href="roiv-20260930.xsd#roiv_AntiFcRnFranchiseEndocrineDiseasesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019febef-edc4-7818-87f9-60fa0737b099" xlink:to="loc_roiv_AntiFcRnFranchiseEndocrineDiseasesMember_019febef-edc4-73b0-96af-e028b6d7cf2a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_AntiFcRnFranchiseNeurologicalDiseasesMember_019febef-edc4-7d0d-a5a7-c8593a991255" xlink:href="roiv-20260930.xsd#roiv_AntiFcRnFranchiseNeurologicalDiseasesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019febef-edc4-7818-87f9-60fa0737b099" xlink:to="loc_roiv_AntiFcRnFranchiseNeurologicalDiseasesMember_019febef-edc4-7d0d-a5a7-c8593a991255" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_AntiFcRnFranchiseRheumatologyDiseasesMember_019febef-edc4-76fc-9c68-c899486ab9e1" xlink:href="roiv-20260930.xsd#roiv_AntiFcRnFranchiseRheumatologyDiseasesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019febef-edc4-7818-87f9-60fa0737b099" xlink:to="loc_roiv_AntiFcRnFranchiseRheumatologyDiseasesMember_019febef-edc4-76fc-9c68-c899486ab9e1" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_AntiFcRnFranchiseDermatologyDiseasesMember_019febef-edc4-74cd-856e-09d3df653f6b" xlink:href="roiv-20260930.xsd#roiv_AntiFcRnFranchiseDermatologyDiseasesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019febef-edc4-7818-87f9-60fa0737b099" xlink:to="loc_roiv_AntiFcRnFranchiseDermatologyDiseasesMember_019febef-edc4-74cd-856e-09d3df653f6b" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_AntiFcRnFranchiseOtherClinicalAndNonclinicalMember_019febef-edc4-79b1-9977-644672365203" xlink:href="roiv-20260930.xsd#roiv_AntiFcRnFranchiseOtherClinicalAndNonclinicalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019febef-edc4-7818-87f9-60fa0737b099" xlink:to="loc_roiv_AntiFcRnFranchiseOtherClinicalAndNonclinicalMember_019febef-edc4-79b1-9977-644672365203" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_BrepocitinibMember_019febef-edc4-70bb-88e3-8bfdda20f1e2" xlink:href="roiv-20260930.xsd#roiv_BrepocitinibMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019febef-edc4-7818-87f9-60fa0737b099" xlink:to="loc_roiv_BrepocitinibMember_019febef-edc4-70bb-88e3-8bfdda20f1e2" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_MosliciguatMember_019febef-edc4-7e05-bb55-b7a7ed95253d" xlink:href="roiv-20260930.xsd#roiv_MosliciguatMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019febef-edc4-7818-87f9-60fa0737b099" xlink:to="loc_roiv_MosliciguatMember_019febef-edc4-7e05-bb55-b7a7ed95253d" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_OtherDevelopmentAndDiscoveryProgramsMember_019febef-edc4-76f6-945a-cf68828982d2" xlink:href="roiv-20260930.xsd#roiv_OtherDevelopmentAndDiscoveryProgramsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019febef-edc4-7818-87f9-60fa0737b099" xlink:to="loc_roiv_OtherDevelopmentAndDiscoveryProgramsMember_019febef-edc4-76f6-945a-cf68828982d2" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019febef-edc4-7a38-8692-4cfc3643d7c5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019febef-edc4-7b11-ae95-87ea83eb0b19" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019febef-edc4-7a38-8692-4cfc3643d7c5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingExpensesAbstract_019febef-edc4-7df5-a7a4-b5e3d0446164" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingExpensesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_019febef-edc4-7b11-ae95-87ea83eb0b19" xlink:to="loc_us-gaap_OperatingExpensesAbstract_019febef-edc4-7df5-a7a4-b5e3d0446164" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfRevenue_019febef-edc4-7d5d-9171-770909dbb4b9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostOfRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019febef-edc4-7df5-a7a4-b5e3d0446164" xlink:to="loc_us-gaap_CostOfRevenue_019febef-edc4-7d5d-9171-770909dbb4b9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpense_019febef-edc4-7a9c-9fff-938eee4bd88b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ResearchAndDevelopmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019febef-edc4-7df5-a7a4-b5e3d0446164" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpense_019febef-edc4-7a9c-9fff-938eee4bd88b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherResearchAndDevelopmentExpense_019febef-edc4-769f-80c3-5ff6622b596a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherResearchAndDevelopmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019febef-edc4-7df5-a7a4-b5e3d0446164" xlink:to="loc_us-gaap_OtherResearchAndDevelopmentExpense_019febef-edc4-769f-80c3-5ff6622b596a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensation_019febef-edc4-73b4-b81c-3e264225e481" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019febef-edc4-7df5-a7a4-b5e3d0446164" xlink:to="loc_us-gaap_ShareBasedCompensation_019febef-edc4-73b4-b81c-3e264225e481" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_PersonnelRelatedExpenses_019febef-edc4-7717-b4cf-6083a8476949" xlink:href="roiv-20260930.xsd#roiv_PersonnelRelatedExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019febef-edc4-7df5-a7a4-b5e3d0446164" xlink:to="loc_roiv_PersonnelRelatedExpenses_019febef-edc4-7717-b4cf-6083a8476949" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherGeneralAndAdministrativeExpense_019febef-edc4-7f83-bbf3-23b9f3704cbd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherGeneralAndAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019febef-edc4-7df5-a7a4-b5e3d0446164" xlink:to="loc_us-gaap_OtherGeneralAndAdministrativeExpense_019febef-edc4-7f83-bbf3-23b9f3704cbd" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LitigationSettlementGain_019febef-edc4-7a45-b70e-fde8f9dbebb9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LitigationSettlementGain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019febef-edc4-7df5-a7a4-b5e3d0446164" xlink:to="loc_us-gaap_LitigationSettlementGain_019febef-edc4-7a45-b70e-fde8f9dbebb9" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnInvestments_019febef-edc4-773b-ad3e-4c09560966e8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainLossOnInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019febef-edc4-7df5-a7a4-b5e3d0446164" xlink:to="loc_us-gaap_GainLossOnInvestments_019febef-edc4-773b-ad3e-4c09560966e8" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_GainLossOnFairValueOfLiabilityInstruments_019febef-edc4-730c-adec-768598f7cf55" xlink:href="roiv-20260930.xsd#roiv_GainLossOnFairValueOfLiabilityInstruments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019febef-edc4-7df5-a7a4-b5e3d0446164" xlink:to="loc_roiv_GainLossOnFairValueOfLiabilityInstruments_019febef-edc4-730c-adec-768598f7cf55" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentIncomeInterest_019febef-edc4-7b51-aea1-2ead99e9437e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentIncomeInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019febef-edc4-7df5-a7a4-b5e3d0446164" xlink:to="loc_us-gaap_InvestmentIncomeInterest_019febef-edc4-7b51-aea1-2ead99e9437e" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_019febef-edc4-71dd-a88e-82c91cee9392" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherNonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019febef-edc4-7df5-a7a4-b5e3d0446164" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_019febef-edc4-71dd-a88e-82c91cee9392" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_019febef-edc4-7b49-a901-527518db1cb2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019febef-edc4-7df5-a7a4-b5e3d0446164" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_019febef-edc4-7b49-a901-527518db1cb2" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTax_01a15420-f025-7064-9df7-1af905df741f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019febef-edc4-7df5-a7a4-b5e3d0446164" xlink:to="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTax_01a15420-f025-7064-9df7-1af905df741f" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_019febef-edc4-781a-ab04-c278ecab40b1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019febef-edc4-7df5-a7a4-b5e3d0446164" xlink:to="loc_us-gaap_ProfitLoss_019febef-edc4-781a-ab04-c278ecab40b1" xlink:type="arc" order="14"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fasb.org/srt/role/srt-eedm/ExtensibleEnumerationLists" xlink:type="simple" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-roles-2026.xsd#eedm1"/>
  <link:definitionLink xlink:role="http://fasb.org/srt/role/srt-eedm/ExtensibleEnumerationLists" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementAbstract"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_GainLossOnFairValueOfLiabilityInstruments_019febef-ec8c-7ded-9842-a03bc2fd266c" xlink:href="roiv-20260930.xsd#roiv_GainLossOnFairValueOfLiabilityInstruments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementAbstract" xlink:to="loc_roiv_GainLossOnFairValueOfLiabilityInstruments_019febef-ec8c-7ded-9842-a03bc2fd266c" xlink:type="arc" order="691"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://xbrl.sec.gov/ecd/role/IndividualsOnly" xlink:type="simple" xlink:href="https://xbrl.sec.gov/ecd/2026/ecd-2026.xsd#IndividualsOnly"/>
  <link:definitionLink xlink:role="http://xbrl.sec.gov/ecd/role/IndividualsOnly" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ecd_AllIndividualsMember" xlink:href="https://xbrl.sec.gov/ecd/2026/ecd-2026.xsd#ecd_AllIndividualsMember"/>
    <link:loc xlink:type="locator" xlink:label="loc_roiv_FrankTortiMember_019febef-edc4-733b-a532-75836eb12b88" xlink:href="roiv-20260930.xsd#roiv_FrankTortiMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ecd_AllIndividualsMember" xlink:to="loc_roiv_FrankTortiMember_019febef-edc4-733b-a532-75836eb12b88" xlink:type="arc" order="2"/>
  </link:definitionLink>
</link:linkbase>
