Company: SLFQF
Filing Date: 2025-02-13
Form Type: 40-F
Source: 0001097362-25-000008
Chunk: 0

Company: SUN LIFE FINANCIAL INC
Filing Date: 2025-02-13
Form: 40-F
Chunk 0
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### UNITED STATES

### SECURITIES AND EXCHANGE COMMISSION

#### Washington, D.C. 20549

#### Form 40-F
| ☐ |     | REGISTRATION STATEMENT PURSUANT TO SECTION 12 OF THE SECURITIES EXCHANGE ACT OF 1934 |

#### OR
| ☒ |     | ANNUAL REPORT PURSUANT TO SECTION 13(a) OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 |

#### For the fiscal year ended December 31, 2024

#### Commission File Number 001-15014

### Sun Life Financial Inc.
<div align='center'>(Exact name of Registrant as specified in its charter)</div>

#### Canada
<div align='center'>(Province or other jurisdiction of incorporation or organization)</div>

#### 52411
<div align='center'>(Primary Standard Industrial Classification Code Number (if applicable))</div>

#### Not Applicable
<div align='center'>(I.R.S. Employer Identification Number (if applicable))

1 York Street, 31 st Floor, Toronto, Ontario, Canada M5J 0B6( 416) 979-9966

(Address and telephone number of Registrant’s principal executive offices)

Sun Life Assurance Company of Canada – U.S. Operations Holdings, Inc.</div>

#### One Sun Life Executive Park

#### Wellesley Hills, Massachusetts 02481
<div align='center'>( 781) 237-6030

(Name, address (including zip code) and telephone number (including area code) of agent for service in the United States)

Securities registered or to be registered pursuant to Section 12(b) of the Act:</div>

| Title of each class |     | Trading Symbol(s) |     | Name of each exchange on which registered |
| Common Shares       |     | SLF               |     | New York Stock Exchange                   |

<div align='center'>Securities registered or to be registered pursuant to Section 12(g) of the Act.</div>

#### Not Applicable
<div align='center'>(Title of Class)

Securities for which there is a reporting obligation pursuant to Section 15(d) of the Act.</div>

#### Not Applicable
<div align='center'>(Title of Class)

For annual reports, indicate by check mark the information filed with this Form:</div>

| ☒Annual information form |     | ☒Audited annual financial statements |

Indicate the number of outstanding