Old City Hall, Ottawa

Old City Hall served as Ottawa's city hall from 1958 to 2000. In 2003, it was acquired by the Government of Canada and renamed after John Diefenbaker, the 13th prime minister of Canada.

Situated on Green Island, where the Rideau River meets the Ottawa River, this building replaced the historic city hall on Elgin Street, which was destroyed by a fire in 1931. During the following 27 years, the city operated from temporary offices in the Transportation Building. On August 2, 1958, Princess Margaret inaugurated the International Style building, making it the first fully air-conditioned structure in Ottawa.

Designed by John Bland of the firm Rother, Bland, and Trudeau, it is recognized as one of Canada's most significant International Style buildings. It received the Massey Medal for design in 1959 and underwent modifications by architect Moshe Safdie in 1992-93.

In 1988, Mayor Jim Durrell expanded the building four times its original size. Architect Moshe Safdie faced conflicts with the city, demanding a higher fee and causing project delays. The city agreed after several months. Another conflict arose over the eighteen-story observation towers. The city council removed the towers to save money, disappointing Safdie. Eventually, a compromise was reached, and a bare scaffold was erected.

On January 1, 2001, the Regional Municipality of Ottawa Carleton was replaced by the new single-tier City of Ottawa. In 2003, the Old City Hall was sold to the federal Public Works Department, and it now primarily accommodates employees from the Department of Foreign Affairs. It also temporarily hosted the Gomery Inquiry hearings for several months.