Arch Capital Group Ltd. (the “issuer”) is offering $aggregate principal amount of% senior notes due 2036 (the “ 2036 notes”) and$aggregate principal amount of% senior notes due 2056 (the “2056 notes” and, together with the 2036 notes, the “notes”). The issuer will payinterest on the notes semi-annually onandof each year, beginning on, 2026. The 2036 notes will mature on,2036 and the 2056 notes matureon, 2056. The maturity date of the notes may be deferred in certain circumstances as described under the caption “Description of Notes—Principal, Interestand Maturity.” The issuer may redeem some or all of the notes at any time at the applicable redemption prices described under the caption “Description ofNotes—Optional Redemption.”The issuer may also redeem all of the Notes under the circumstances described under the heading “Description of Notes—Redemptionfor Tax Purposes.”Notwithstanding the foregoing, the notes will not be redeemable at any time, including at any applicable maturity date, unless the Conditionsto Redemption (as defined herein) have been satisfied and will continue to be satisfied immediately before or after giving effect to the redemption of suchnotes. The issuer intends to use the net proceeds from this offering to redeem, repurchase, repay or otherwise retire the 2026 Existing Notes (as defined herein)and finance the Tender Offers (as defined herein). Any net proceeds not used for the foregoing will be used for general corporate purposes. See “Use ofProceeds.” The notes will be senior unsecured obligations of the issuer, will rank equally with any of the issuer’s senior unsecured and unsubordinated indebtednessfrom time to time outstanding, be senior in right of payment to our future indebtedness that is expressly subordinated in right of payment to the notes, beeffectively subordinated to all secured indebtedness of the issuer to the extent of the value of the assets securing such indebtedness; be effectively subordinatedto all existing and future obligations (including amounts owed to holders of reinsurance and insurance policies) of the issuer’s subsidiaries and not beguaranteed by any of the issuer’s subsidiaries. The issuer does not intend to apply for listing of the notes on any securities exchange or quotation on anyautomated quotation system. An investment in the notes involves risks. See “Risk Factors” beginning on pageS-10of this prospectus supplement to read about important factors youshould consider before investing in the notes. (1)Plus accrued interest, if any, from , 2026 if settlement occurs after that date.The underwriters expect to deliver the notes in book-entry form only through the facilities of The Depository Trust Company (“DTC”) against paymentin New York, New York on or about,2026. Lloyds Securities RBC Capital Markets The date of this prospectus supplement is, 2026. TABLE OF CONTENTS Prospectus SupplementAbout This Prospectus SupplementS-1Prospectus Supplement SummaryS-4Risk FactorsS-10Use of ProceedsS-14Description of NotesS-15Book-Entry; Delivery and FormS-31Certain United States Federal Income Tax Consequences to U.S. HoldersS-33Certain ERISA ConsiderationsS-36Underwriting (Conflicts of Interest)S-38Legal MattersS-43ExpertsS-43Cautionary Note Regarding Forward-Looking StatementsS-44Where You Can Find Additional InformationS-46 PageProspectusArch Capital GroupLtd.1Arch Capital Group (U.S.)Inc.1Arch Capital Finance LLC1About This Prospectus1Risk Factors2Use of Proceeds2Description of Arch Capital Share Capital2Description of Arch Capital Debt Securities4Description of Arch Capital Depositary Shares4Description of Arch Capital Warrants to Purchase Common Shares or Preference Shares4Description of Arch Capital Warrants to Purchase Debt Securities5Description of Arch Capital Share Purchase Contracts and Share Purchase Units5Description of Arch Capital Group (U.S.)Inc. Preferred Stock5Description of Arch Capital Group (U.S.)Inc. Unsecured Debt Securities6Description of Arch Capital Finance LLC Unsecured Debt Securities6Selling Shareholders7Plan of Distribution7Where You Can Find More Information8Incorporation of Documents by Reference8Cautionary Note Regarding Forward-Looking Statements9Legal Matters10Independent Registered Public Accounting Firm10Enforcement of Civil Liabilities Under United States Federal Securities Laws10 ABOUT THIS PROSPECTUS SUPPLEMENT This document is in two parts. The first part is this prospectus supplement, which describes the specific terms of this offering,including risk factors and material tax considerations, and also adds to and updates information contained in the accompanyingprospectus and the documents incorporated by reference herein. The second part is the accompanying prospectus, which gives moregeneral information, some of which may not apply to this offering. It is important for you to read and consider all informationcontained in this prospectus supplement, the accompanying prospectus and the documents incorporated b