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

    <schemaVersion>X0508</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2025-01-09</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001083301</issuerCik>
        <issuerName>TERAWULF INC.</issuerName>
        <issuerTradingSymbol>WULF</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001877255</rptOwnerCik>
            <rptOwnerName>Prager Paul B.</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O TERAWULF INC.</rptOwnerStreet1>
            <rptOwnerStreet2>9 FEDERAL STREET</rptOwnerStreet2>
            <rptOwnerCity>EASTON</rptOwnerCity>
            <rptOwnerState>MD</rptOwnerState>
            <rptOwnerZipCode>21601</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Chief Executive Officer</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <aff10b5One>0</aff10b5One>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common stock, $0.001 par value per share</value>
            </securityTitle>
            <transactionDate>
                <value>2025-01-09</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>500000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>1885700</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common stock, $0.001 par value per share</value>
            </securityTitle>
            <transactionDate>
                <value>2025-01-09</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>D</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>276500</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F2"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>1609200</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common stock, $0.001 par value per share</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>260513</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Beowulf Electricity &amp; Data Inc.</value>
                    <footnoteId id="F3"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common stock, $0.001 par value per share</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>5000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Heorot Power Holdings LLC</value>
                    <footnoteId id="F4"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common stock, $0.001 par value per share</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>654706</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Lucky Liefern LLC</value>
                    <footnoteId id="F5"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common stock, $0.001 par value per share</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>21100000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Riesling Power LLC</value>
                    <footnoteId id="F6"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common stock, $0.001 par value per share</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>1598883</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Stammtisch Investments LLC</value>
                    <footnoteId id="F7"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Restricted Stock Units</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F8"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2025-01-09</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>M</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>500000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F9"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F9"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F9"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common stock, $0.001 par value per share</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>500000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">The Reporting Person received restricted stock units which vested in accordance with their terms upon the first anniversary of January 9, 2024, as reflected in this Form 4, subject to the Reporting Person's continued employment or service with the Issuer through such date.</footnote>
        <footnote id="F2">The disposition is due to withholding to cover taxes, as a result of the Reporting Person's election of net settlement with regard to the vesting of restricted stock units, which vested on January 9, 2025, as reflected in this Form 4.</footnote>
        <footnote id="F3">By Beowulf Electricity &amp; Data Inc. (&quot;Beowulf E&amp;D&quot;) The Reporting Person is the sole shareholder of Beowulf E&amp;D and, as a result, may be deemed to beneficially own the shares of the Issuer's common stock, par value $.001 per share (&quot;Common Stock&quot;) held by Beowulf E&amp;D. The Reporting Person disclaims beneficial ownership of such shares of Common Stock except to the extent of his pecuniary interest therein, and the inclusion of such shares of Common Stock in this report shall not be deemed an admission of beneficial ownership of all of the reported shares of Common Stock for purposes of Section 16 of the Exchange Act of 1934, as amended (the &quot;Exchange Act&quot;), or for any other purpose.</footnote>
        <footnote id="F4">By Heorot Power Holdings LLC (&quot;Heorot&quot;). The Reporting Person is the sole manager of Heorot and, as a result, may be deemed to beneficially own the shares of the Common Stock held by Heorot. The Reporting Person disclaims beneficial ownership of such shares of the Common Stock except to the extent of his pecuniary interest therein, and the inclusion of such shares of the Common Stock in this report shall not be deemed an admission of beneficial ownership of all of the reported shares of the Common Stock for purposes of Section 16 of the Exchange Act, or for any other purpose.</footnote>
        <footnote id="F5">By Lucky Liefern LLC. The Reporting Person is the sole manager of Lucky Liefern LLC and, as a result, may be deemed to beneficially own the shares of the Common Stock held by Lucky Liefern LLC. The Reporting Person disclaims beneficial ownership of such shares of the Common Stock except to the extent of his pecuniary interest therein, and the inclusion of such shares of the Common Stock in this report shall not be deemed an admission of beneficial ownership of all of the reported shares of the Common Stock for purposes of Section 16 of the Exchange Act, or for any other purpose.</footnote>
        <footnote id="F6">By Riesling Power LLC (&quot;Riesling Power&quot;). The Paul B. Prager Revocable Trust (&quot;Prager Revocable Trust&quot;) is the sole member of Riesling Power. The Reporting Person is the sole trustee of the Prager Revocable Trust and may be deemed to have the power to direct the voting and disposition of the Common Stock beneficially owned by the Prager Revocable Trust. Accordingly, pursuant to the regulations promulgated under Section 13(d) of the Exchange Act, Mr. Paul B. Prager may be deemed to be a beneficial owner of the shares of Common Stock held for the account of the Prager Revocable Trust .</footnote>
        <footnote id="F7">By Stammtisch Investments LLC (&quot;Stammtisch&quot;). The Reporting Person is the sole manager of Stammtisch and, as a result, may be deemed to beneficially own the shares of Common Stock held by Stammtisch. The Reporting Person disclaims beneficial ownership of such shares of Common Stock except to the extent of his pecuniary interest therein, and the inclusion of such shares of Common Stock in this report shall not be deemed an admission of beneficial ownership of all of the reported shares of Common Stock for purposes of Section 16 of the Exchange Act, or for any other purpose.</footnote>
        <footnote id="F8">Each restricted stock unit represents a contingent right to receive one share of the Issuer's Common Stock.</footnote>
        <footnote id="F9">The restricted stock units vested upon the first anniversary of January 9, 2024, subject to the Reporting Person's continued employment or service with the Issuer through such date.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Paul B. Prager</signatureName>
        <signatureDate>2025-01-10</signatureDate>
    </ownerSignature>
</ownershipDocument>
