UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

Current Report

Pursuant To Section 13 or 15 (d) of the

Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): May 16, 2013

ACE LIMITED

(Exact name of registrant as specified in its charter)

Baerengasse 32

CH-8001 Zurich, Switzerland

(Address of principal executive offices)

Registrant’s telephone number, including area code: +41 (0)43 456 76 00

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions (see General Instruction A.2. below):

¨ Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

¨ Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

¨ Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

¨ Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

(e) At the company’s 2013 annual general meeting, the company’s shareholders approved the ACE Limited 2004 Long-Term Incentive Plan, as amended through the sixth amendment, (the “LTIP”) increasing the number of common shares reserved for delivery under the LTIP by 8,000,000 shares, which shares are in addition to the 30,600,000 common shares previously reserved under the LTIP. In addition to increasing the number of common shares available for issuance, the sixth amendment also increased by 3,200,000 shares the sublimit that restricts the ability to grant “full value awards” under the LTIP. A more complete description of the LTIP is contained in company’s proxy statement, dated April 5, 2013, as filed with the Securities and Exchange Commission, under the heading “Agenda Item No. 7: Approval of ACE Limited 2004 Long-Term Incentive Plan as Amended through the Sixth Amendment,” which is hereby incorporated herein by reference. For the full text of the LTIP, see Exhibit 10.1 hereto, which is hereby incorporated herein by reference.

At the company’s 2013 annual general meeting, the company’s shareholders approved an amendment to Article 17(a) of the Articles of Association to authorize the declassification of the company’s board of directors commencing at the company’s annual general meeting in 2014, at which time directors will stand for election for one-year terms. Directors who were elected at the company’s 2013 or 2012 annual general meetings whose terms will expire in 2015 or 2016 will continue to hold office until the end of the terms for which they were elected. All directors will be elected on an annual basis beginning with the company’s 2016 annual general meeting, as further described in the company’s proxy statement dated April 5, 2013, under the heading “Agenda Item No.2: Approval of the Articles of Association to Declassify the Board of Directors.” Such amendment to Article 17(a) of the Articles of Association will become effective with its registration in the Commercial Register of the Canton of Zurich, Switzerland (the “Swiss Commercial Register”). Filing of the Articles of Association with the Swiss Commercial Register occurred on May 17, 2013 and registration is expected to be effective on or about May 21, 2013.

At the company’s 2013 annual general meeting, the company’s shareholders also prospectively approved amendments to the company’s Articles of Association in conjunction with their approval of payments of a dividend in the form of distribution through par value reduction, as further described in the company’s proxy statement dated April 5, 2013, under the heading “Agenda Item No.8: Approval of Distribution to Shareholders in the Form of Par Value Reduction.” Such amendments will become effective with the registration of each quarterly par value reduction in the Swiss Commercial Register.

A copy of the amended Articles of Association is attached hereto as Exhibit 3.1 and incorporated herein by reference.

On May 16, 2013, the board of directors of the company amended Section 7 of the company’s Organizational Regulations primarily to reflect the changes to the compensation committee’s authority, duties and responsibilities required by the amended listing standards of the New York Stock Exchange. A copy of the amended Organizational Regulations is attached hereto as Exhibit 3.2 and incorporated herein by reference.

The company convened its annual general meeting of shareholders on May 16, 2013 pursuant to notice duly given. The matters voted upon at the meeting and the results of such voting are set forth below:

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The voting results for Agenda Item No. 5 exclude shares held by the company’s directors and executive officers, who are not permitted by law to vote their shares on the discharge of the Board of Directors.

Under the company’s Articles of Association, shareholder approval of proposals is generally determined by simple majority of votes cast, such that abstentions and broker non-votes are disregarded in the tabulation of the vote to determine approval. At the 2013 annual general meeting, abstentions and broker non-votes were not considered in the tabulation of the vote (and thus should be disregarded) to determine approval of each of the items above.

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(d) Exhibits

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SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the Registrant has duly caused this report to be signed on its behalf by the undersigned thereunto duly authorized.

DATE: May 20, 2013

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