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<!-- DFIN ActiveDisclosure(SM) XBRL Schema Document - http://www.dfinsolutions.com/ -->
<!-- Creation Date      : 2021-03-15T20:15:11.2803470+00:00 -->
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<!-- Package ID         : 95d8400a2c424ccabf3eab8806cd8375 -->
<!-- Copyright (c) 2021 Donnelley Financial Solutions, Inc. All Rights Reserved. -->
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  <xsd:element id="ngm_ShareOfGlobalDevelopmentCostsPercentage" name="ShareOfGlobalDevelopmentCostsPercentage" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ngm_LicenseFeeReceivable" name="LicenseFeeReceivable" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="ngm_ResearchAndDevelopmentOptionExtendTerm" name="ResearchAndDevelopmentOptionExtendTerm" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ngm_ResearchAndDevelopmentServicePerformancePeriod" name="ResearchAndDevelopmentServicePerformancePeriod" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ngm_NumberOfOptionsToExtendPerformanceOfResearchProgram" name="NumberOfOptionsToExtendPerformanceOfResearchProgram" type="xbrli:integerItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" />
  <xsd:element id="ngm_ReceivedAmountFromOptions" name="ReceivedAmountFromOptions" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="ngm_UpfrontFee" name="UpfrontFee" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="ngm_CollaborativeArrangementAnnualFundingAmountOverAgreementTerm" name="CollaborativeArrangementAnnualFundingAmountOverAgreementTerm" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="ngm_CollaborativeAgreementConsiderationMilestone" name="CollaborativeAgreementConsiderationMilestone" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="ngm_RevenueTransactionPrice" name="RevenueTransactionPrice" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="ngm_MilestonePaymentForPotentialAchievementOfCertainClinicalDevelopmentEvents" name="MilestonePaymentForPotentialAchievementOfCertainClinicalDevelopmentEvents" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="ngm_ResearchCollaborationAndLicenseAgreementsAbstract" name="ResearchCollaborationAndLicenseAgreementsAbstract" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ngm_FirstIndicationMember" name="FirstIndicationMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ngm_SecondIndicationMember" name="SecondIndicationMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ngm_ThirdIndicationMember" name="ThirdIndicationMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ngm_ClinicalTrialToFirstPatientInFirstPhaseThreeMember" name="ClinicalTrialToFirstPatientInFirstPhaseThreeMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ngm_MilestonePaymentForPotentialAchievementOfCertainRegulatoryEvents" name="MilestonePaymentForPotentialAchievementOfCertainRegulatoryEvents" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="ngm_DisclosureResearchCollaborationAndLicenseAgreementsScheduleOfRecognizedRevenueFromCollaborationAndLicenseAgreementsDetailsAbstract" name="DisclosureResearchCollaborationAndLicenseAgreementsScheduleOfRecognizedRevenueFromCollaborationAndLicenseAgreementsDetailsAbstract" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ngm_UpfrontLicenseFee" name="UpfrontLicenseFee" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="ngm_AmortizationOfUpfrontPayments" name="AmortizationOfUpfrontPayments" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="ngm_OperatingLeaseExpirationPeriod" name="OperatingLeaseExpirationPeriod" type="xbrli:gYearMonthItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ngm_ReductionInSecurityDeposit" name="ReductionInSecurityDeposit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="ngm_CommitmentsAndContingenciesDisclosureLineItems" name="CommitmentsAndContingenciesDisclosureLineItems" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ngm_CommitmentsAndContingenciesDisclosureTable" name="CommitmentsAndContingenciesDisclosureTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ngm_CorporateOfficeSpaceAndLaboratoryFacilityMember" name="CorporateOfficeSpaceAndLaboratoryFacilityMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ngm_LandlordAndMerckMember" name="LandlordAndMerckMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ngm_OperatingLeaseAgreementAmendmentPeriod" name="OperatingLeaseAgreementAmendmentPeriod" type="xbrli:gYearMonthItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ngm_StockOptionFiscalTwentyEighteenPlanMember" name="StockOptionFiscalTwentyEighteenPlanMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ngm_TenPercentOrGreaterStockholderMember" name="TenPercentOrGreaterStockholderMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ngm_EmployeesAndDirectorsMember" name="EmployeesAndDirectorsMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ngm_ReserveBalanceForSalesAgreementMember" name="ReserveBalanceForSalesAgreementMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ngm_FourZeroOneKMatchingPlanMember" name="FourZeroOneKMatchingPlanMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ngm_CommonStockOptionsOutstandingMember" name="CommonStockOptionsOutstandingMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ngm_CommonStockOptionsAvailableForGrantMember" name="CommonStockOptionsAvailableForGrantMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ngm_SaleOfCommonStockAggregatePrice" name="SaleOfCommonStockAggregatePrice" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="ngm_CommonStockAvailableToBeIssuance" name="CommonStockAvailableToBeIssuance" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" />
  <xsd:element id="ngm_SalesCommissions" name="SalesCommissions" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="ngm_PercentageOfNumberOfSharesReservedAndAvailableToIssueAutomaticallyIncreaseOutstandingOnPrecedingCalendar" name="PercentageOfNumberOfSharesReservedAndAvailableToIssueAutomaticallyIncreaseOutstandingOnPrecedingCalendar" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ngm_OfferingPeriodForPurchaseUnderEmployeeStockPurchasePlan" name="OfferingPeriodForPurchaseUnderEmployeeStockPurchasePlan" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ngm_NumberOfPurchasePeriods" name="NumberOfPurchasePeriods" type="xbrli:integerItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ngm_DurationOfEachPurchasePeriod" name="DurationOfEachPurchasePeriod" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ngm_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAvailableForGrantsInPeriod" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAvailableForGrantsInPeriod" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ngm_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAvailableForGrantExercisedInPeriod" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAvailableForGrantExercisedInPeriod" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ngm_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAvailableForGrantForfeituresInPeriod" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAvailableForGrantForfeituresInPeriod" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ngm_SharesRightToRepurchaseLapsePeriod" name="SharesRightToRepurchaseLapsePeriod" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ngm_ShareRepurchaseProgramRepurchasePricePerShare" name="ShareRepurchaseProgramRepurchasePricePerShare" type="num:perShareItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" />
  <xsd:element id="ngm_EarlyExerciseOfStockOptionLiabilities" name="EarlyExerciseOfStockOptionLiabilities" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="ngm_DeferredTaxAssetsContractLiabilities" name="DeferredTaxAssetsContractLiabilities" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="ngm_DeferredTaxLiabilitiesDepreciationAndAmortization" name="DeferredTaxLiabilitiesDepreciationAndAmortization" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="ngm_DeferredTaxLiabilitiesNonQualifiedStockOptions" name="DeferredTaxLiabilitiesNonQualifiedStockOptions" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="ngm_DeferredTaxAssetsNetBeforeValuationAllowance" name="DeferredTaxAssetsNetBeforeValuationAllowance" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="ngm_IncomeTaxDisclosureLineItems" name="IncomeTaxDisclosureLineItems" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ngm_IncomeTaxDisclosureTable" name="IncomeTaxDisclosureTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="ngm_NetOperatingLossCarryforwardsExpirationPeriod" name="NetOperatingLossCarryforwardsExpirationPeriod" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ngm_NetOperatingLossCarryforwardsExpirationYear" name="NetOperatingLossCarryforwardsExpirationYear" type="us-types:gYearListItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ngm_PercentageOfNetOperatingLossCarryforwardsUtilizationLimitOfTaxableIncomeSubsequentToEnactmentOfTwoThousandSeventeenTaxAct" name="PercentageOfNetOperatingLossCarryforwardsUtilizationLimitOfTaxableIncomeSubsequentToEnactmentOfTwoThousandSeventeenTaxAct" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ngm_ResearchAndDevelopmentCreditsExpirationYear" name="ResearchAndDevelopmentCreditsExpirationYear" type="us-types:gYearListItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="ngm_AdditionalCommonStockOptionToPurchase" name="AdditionalCommonStockOptionToPurchase" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
</xsd:schema>
