From 1881 to 1896, he was Chief Dominion Architect for the Government of Canada, during which time he played a role in the design and construction of every major federal building.

[4] In 1859, the Legislative Assembly in Ottawa voted the sum of £75,000 for the erection of a "Parliament House" and offered a premium of $1000 for the best design within that budget.

In Hand Book to the Parliamentary and Departmental Buildings, Canada (1867), Joseph Bureau wrote, "The corner stone was laid with great ceremony by His Royal Highness the Prince of Wales [the future king Edward VII] in September 1860, on which occasion the rejoicings partook of the nature of the place, the lumber arches and men being a novelty to most of its visitors, bullocks and sheep were roasted whole upon the government ground and all comers were feasted."

Fuller thus returned to Canada and, unable to work in the more lucrative private sector, in 1881 became Chief Dominion Architect, succeeding Thomas Seaton Scott.

Canada's Department of Public Works erected a number of post offices in smaller urban centres during Thomas Fuller's term as chief architect.