HALO: amended insider filing

<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0609</schemaVersion>

    <documentType>4/A</documentType>

    <periodOfReport>2026-05-05</periodOfReport>

    <dateOfOriginalSubmission>2026-05-07</dateOfOriginalSubmission>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001159036</issuerCik>
        <issuerName>HALOZYME THERAPEUTICS, INC.</issuerName>
        <issuerTradingSymbol>HALO</issuerTradingSymbol>
        <issuerForeignTradingSymbol></issuerForeignTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001662521</rptOwnerCik>
            <rptOwnerName>Connaughton Bernadette</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerNonUSAddressFlag>false</rptOwnerNonUSAddressFlag>
            <rptOwnerStreet1>C/O HALOZYME THERAPEUTICS, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>12390 EL CAMINO REAL</rptOwnerStreet2>
            <rptOwnerCity>SAN DIEGO</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>92130</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <aff10b5One>0</aff10b5One>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2026-05-05</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>3796</value>
                    <footnoteId id="F1"/>
                    <footnoteId id="F2"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>42294</value>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">Represents annual restricted stock unit (&quot;RSU&quot;) grant under the Issuer's director compensation program. Each RSU represents the right to receive one share of common stock of the Issuer. This grant will vest in full on the earlier of (i) May 5, 2027 and (ii) the date of the Issuer's next annual meeting of stockholders.</footnote>
        <footnote id="F2">This Form 4/A amends the Form 4 filed on May 7, 2026 solely to correct the number of RSUs acquired and the amount of securities beneficially owned following the reported transaction. The original filing reported 6,796 RSUs acquired. The correct number of RSUs acquired was 3,796. As a result, the amount of securities beneficially owned following the transaction has been revised accordingly.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ James R. Oehler, Attorney-in-Fact</signatureName>
        <signatureDate>2026-10-08</signatureDate>
    </ownerSignature>
</ownershipDocument>