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UNITED STATESSECURITIES AND EXCHANGE COMMISSIONWashington, D.C.
20549

FORM 40-F/A(Amendment No.1)

(Check One)

[   ] Registration statement pursuant to Section 12 of
the Securities Exchange Act of 1934 or

[X] Annual report pursuant to section 13(a) or 15(d) of the
Securities Exchange Act of 1934

For the fiscal year ended December 31, 2017

Commission file number001-36596

TRILLIUM THERAPEUTICS INC.(Exact name of registrant as specified in its charter)

|Ontario, Canada                    | 2834                                       | Not applicable                        
|---------------------------------- | ------------------------------------------ | --------------------------------------
|(Province or other jurisdiction of | (Primary Standard Industrial               | (I.R.S. Employer                      
|incorporation or organization)     | Classification Code Number(if applicable)) | Identification Number (if applicable))

2488 Dunwin Drive, Mississauga, Ontario, Canada L5L 1J9
Telephone: (416) 595-0627(Address and Telephone Number of
Registrants Principal Executive Offices)

Puglisi & Associates, 850 Library Avenue, Suite 204,
Newark, Delaware 19711 Telephone: (302) 738-6680(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.

|Title of each class | Name of each exchange on which
      registered
|------------------- | -----------------------------------------------
|Common Shares       | The NASDAQ Stock Market LLC                    

Securities registered or to be registered pursuant to Section
12(g) of the Act. None

Securities for which there is a reporting obligation pursuant to
Section 15(d) of the Act. None

For annual reports, indicate by check mark the information filed
with this Form:

|[X] Annual Information Form | [X] Audited Annual Financial Statements
|--------------------------- | ---------------------------------------

Indicate the number of outstanding shares of each of the
issuers classes of capital or common stock as of the close of the period
covered by the annual report: 13,147,404 common shares

Indicate by check mark whether the registrant: (1) has filed
all reports required to be filed by Section 13 or 15(d) of the Securities
Exchange Act of 1934 (the Exchange Act) during the preceding 12 months (or for
such shorter period that the registrant was required to file such reports); and
(2) has been subject to such filing requirements for the past 90 days.

Yes [X]       No [  
]

Indicate by check mark whether the registrant has submitted
electronically and posted on its corporate Web site, if any, every Interactive
Data File required to be submitted and posted pursuant to Rule 405 of Regulation
S-T (s.232.405 of this chapter) during the preceding 12 months (or for such
shorter period that the registrant was required to submit and post such files).

Yes  [   ]      
No  [   ]

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Indicate by check mark whether the registrant is an emerging
growth company as defined in Rule 12b-2 of the Exchange Act.

Emerging growth company [X]

If an emerging growth company that prepares its financial
statements in accordance with U.S. GAAP, indicate by check mark if the
registrant has elected not to use the extended transition period for complying
with any new or revised financial accounting standards provided pursuant to
Section 13(a) of the Exchange Act. [   ]

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EXPLANATORY NOTE

Trillium Therapeutics Inc. (the
Corporation) is filing this Form 40-F/A to the Corporations Annual Report on
Form 40-F dated March 9, 2018 (the Form 40-F), for the sole purpose of
re-filing Exhibit 99.3 (Audited Consolidated Financial Statements for the years
ended December 31, 2017 and 2016, prepared under International Financial
Reporting Standards as issued by the International Accounting Standards Board)
which inadvertently omitted the signature of Ernst & Young LLP to its Report of
Independent Registered Public Accounting Firm.

Other than the correction to the Report
of Independent Registered Public Accounting Firm included as part of Exhibit
99.3, no other changes have been made to the Form 40-F. This Form 40-F/A speaks
as of the original time of filing the Form 40-F, does not reflect events that
may have occurred subsequent to such filing, and does not modify or update in
any way disclosures made in the Form 40-F.

US-1

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SIGNATURES

Pursuant to the requirements of the
Exchange Act, Trillium Therapeutics Inc. certifies that it meets all of the
requirements for filing on Form 40-F and has duly caused this annual report to
be signed on its behalf by the undersigned, thereunto duly authorized, on March
12, 2018.

Trillium Therapeutics Inc.By:
    /s/ James ParsonsName: James ParsonsTitle: Chief Financial Officer


US-2

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EXHIBIT INDEX

|Exhibit | Description                                                                                                                                                                                                         
|------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|        |                                                                                                                                                                                                                     
|99.1*   | Annual Information Form for the fiscal year ended December 31, 2017                                                                                                                                                 
|        |                                                                                                                                                                                                                     
|99.2*   | Management’s Discussion and Analysis for the years ended December 31, 2017 and 2016                                                                                                                                 
|        |                                                                                                                                                                                                                     
|99.3    | Audited Consolidated Financial Statements for the years ended December 31,
	  2017 and 2016, prepared under International Financial Reporting Standards as
	  issued by the International Accounting Standards Board
|        |                                                                                                                                                                                                                     
|99.4    | Certification of President & Chief Executive Officer pursuant to Rule 13a-14(a)
	  or 15d-14 of the Securities Exchange Act of 1934                                                                                 
|        |                                                                                                                                                                                                                     
|99.5    | Certification of Chief Financial Officer pursuant to Rule 13a-14(a) or 15d-14 of
	  the Securities Exchange Act of 1934                                                                                             
|        |                                                                                                                                                                                                                     
|99.6    | Certification of Chief Executive Officer pursuant to 18 U.S.C. Section 1350                                                                                                                                         
|        |                                                                                                                                                                                                                     
|99.7    | Certification of Chief Financial Officer pursuant to 18 U.S.C. Section 1350                                                                                                                                         
|        |                                                                                                                                                                                                                     
|99.8*   | Consent of Ernst & Young LLP                                                                                                                                                                                        

*Previously filed with the Commission.

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