UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 14A

(Rule 14a-101)

INFORMATION REQUIRED IN PROXY STATEMENT

SCHEDULE 14A INFORMATION

Proxy Statement Pursuant to Section 14(a) of the Securities Exchange Act of 1934

(Amendment No. )

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Filed by a Party other than the Registrant ☒

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☐ Preliminary Proxy Statement

☐ Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2))

☐ Definitive Proxy Statement

☒ Definitive Additional Materials

☐ Soliciting Material Under § 240.14a-12

ARGO GROUP INTERNATIONAL HOLDINGS, LTD.

(Name of Registrant as Specified In Its Charter)

CAPITAL RETURNS MASTER, LTD.

CAPITAL RETURNS MANAGEMENT, LLC

THE CAPITAL RETURNS 2016 FAMILY TRUST

RONALD D. BOBMAN

DAVID W. MICHELSON

(Name of Persons(s) Filing Proxy Statement, if other than the Registrant)

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Capital Returns Master, Ltd., a Cayman Islands exempted company, together with the other participants named herein (collectively, “Capital Returns”), has filed a definitive proxy statement and accompanying WHITE universal proxy card with the Securities and Exchange Commission in connection with the 2022 annual general meeting of shareholders (the “Annual General Meeting”) of Argo Group International Holdings, Ltd., a Bermuda exempted company limited by shares (the “Company”), to be used to solicit votes for the election of Capital Returns’ slate of highly qualified nominees at the Annual General Meeting.

On November 14, 2022, Capital Returns issued an Investor Presentation titled “Enhancing Shareholder Value with New Board Members,” a copy of which is attached hereto as Exhibit 1 and is incorporated herein by reference.