Company: ACCO
Filing Date: 2025-03-31
Form Type: DEFA14A
Source: 0000950170-25-046988
Chunk: 0

Company: ACCO BRANDS Corp
Filing Date: 2025-03-31
Form: DEFA14A
Chunk 0
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<div align='center'>UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D. C. 20549

SCHEDULE 14A INFORMATION

Proxy Statement Pursuant to Section 14(a) of the

Securities Exchange Act of 1934</div>

| Filed by the Registrant ☒ | ​ | ​ | Filed by a party other than the Registrant  ☐ |

Check the appropriate box:

| ☐ | ​ | ​ | 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                                           |

<div align='center'>ACCO BRANDS CORPORATION

(Name of Registrant as Specified in Its Charter)

(Name of Person(s) Filing Proxy Statement, if other than the Registrant)</div>

Payment of Filing Fee (Check all boxes that apply):

| ☒ | ​ | ​ | No fee required                                                                                     |
| ☐ | ​ | ​ | Fee paid previously with preliminary materials                                                      |
| ☐ | ​ | ​ | Fee computed on table in exhibit required by Item 25(b) per Exchange Act Rules 14a-6(i)(1) and 0-11 |

<div align='center'>EXPLANATORY NOTE</div>

ACCO Brands Corporation (the “Company”) is filing this supplement to its definitive proxy statement (“Proxy Statement”) for its 2025 Annual Meeting of Stockholders (“Annual Meeting”) to correct a typographical error in certain website addresses contained in the Notice of 2025 Annual Meeting of Stockholders (“Meeting Notice”) included with the introductory pages of the Proxy Statement. The corrected website addresses are reflected in the Meeting Notice set forth below.

Please be advised that the website addresses contained in the NoticeRegarding the Availability of Proxy Materials mailed to Company stockholders are correct. Except as specifically set forth in this Supplement, all information set forth in the Proxy Statement remains unchanged.

<div align='center'>See following page for corrected information.</div>

| Notice of 2025 Annual Meeting of Stockholders 
 Location:                                     | Date & Time: | Virtual at : https://web.viewproxy.com/ACCO/2025 | Tuesday, May 20,