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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2017-12-29</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000783325</issuerCik>
        <issuerName>WEC ENERGY GROUP, INC.</issuerName>
        <issuerTradingSymbol>WEC</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001506822</rptOwnerCik>
            <rptOwnerName>Guc William J</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>231 WEST MICHIGAN STREET</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>MILWAUKEE</rptOwnerCity>
            <rptOwnerState>WI</rptOwnerState>
            <rptOwnerZipCode>53203</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Vice President &amp; Controller</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable></nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Phantom Stock Units</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F1"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2017-12-29</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>124.7629</value>
                    <footnoteId id="F2"/>
                    <footnoteId id="F3"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>66.43</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F4"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F4"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>124.7629</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>130.2936</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
        <derivativeTransaction>
            <securityTitle>
                <value>Phantom Stock Units</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F1"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2018-02-02</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>2.8947</value>
                    <footnoteId id="F5"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>62.01</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F4"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F4"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>2.8947</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>133.1883</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">One-for-one</footnote>
        <footnote id="F2">These phantom stock units were acquired as the result of a &quot;make-whole&quot; payment for compensation not otherwise eligible for matching in a WEC Energy Group 401(k) plan due to limits imposed by the Internal Revenue Code in an acquisition exempt from Section 16(b) pursuant to Rule 16b-3(d).</footnote>
        <footnote id="F3">This transaction is being reported late due to an administrative error.  These units were omitted from the reporting person's Form 4 filed on January 23, 2018.</footnote>
        <footnote id="F4">These phantom stock units were accrued under the WEC Energy Group, Inc. Executive Deferred Compensation Plan and are to be settled following the reporting person's retirement or other termination of employment.</footnote>
        <footnote id="F5">These phantom stock units were acquired pursuant to a deferral of compensation in an acquisition exempt from Section 16(b) pursuant to Rule 16b-3(d).</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Joshua M. Erickson, as attorney in fact</signatureName>
        <signatureDate>2018-02-06</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0306
4
2017-12-29
0
0000783325
WEC ENERGY GROUP, INC.
WEC
0001506822
Guc William J
231 WEST MICHIGAN STREET
MILWAUKEE
WI
53203
0
1
0
0
Vice President & Controller
Phantom Stock Units
2017-12-29
4
A
0
124.7629
66.43
A
Common Stock
124.7629
130.2936
D
Phantom Stock Units
2018-02-02
4
A
0
2.8947
62.01
A
Common Stock
2.8947
133.1883
D
One-for-one
These phantom stock units were acquired as the result of a "make-whole" payment for compensation not otherwise eligible for matching in a WEC Energy Group 401(k) plan due to limits imposed by the Internal Revenue Code in an acquisition exempt from Section 16(b) pursuant to Rule 16b-3(d).
This transaction is being reported late due to an administrative error.  These units were omitted from the reporting person's Form 4 filed on January 23, 2018.
These phantom stock units were accrued under the WEC Energy Group, Inc. Executive Deferred Compensation Plan and are to be settled following the reporting person's retirement or other termination of employment.
These phantom stock units were acquired pursuant to a deferral of compensation in an acquisition exempt from Section 16(b) pursuant to Rule 16b-3(d).
Joshua M. Erickson, as attorney in fact
2018-02-06