What is Canada's supreme governing document?

Canada's supreme governing document is the Constitution of Canada, a set of constitutional documents and unwritten conventions that together establish the framework of Canadian government, the division of powers, and the protected rights of Canadians. The Constitution is supreme law: under section 52(1) of the Constitution Act, 1982, any law inconsistent with the Constitution is, to the extent of the inconsistency, of no force or effect. The Supreme Court of Canada is the final arbiter of constitutional interpretation.

The Constitution has two principal written components. The Constitution Act, 1867 (originally the British North America Act, 1867) is the founding document of Canadian Confederation, passed by the British Parliament on March 29, 1867 and entered into force on July 1, 1867. It establishes Parliament, the Senate, the House of Commons, the office of the Governor General, the federal-provincial division of powers in sections 91 and 92, and the structure of the courts in sections 96 to 101. The Constitution Act, 1982, brought into force on April 17, 1982 by Queen Elizabeth II in Ottawa, patriated the Constitution from the United Kingdom and added the Canadian Charter of Rights and Freedoms (Part I), section 35 Indigenous rights protection (Part II), and an amending formula (Part V).

Beyond these two principal Acts, the Constitution includes about 30 other documents listed in the schedule to the Constitution Act, 1982. These include the Manitoba Act of 1870, the Alberta Act and Saskatchewan Act of 1905, the Newfoundland Act of 1949, and various treaties and proclamations. The Royal Proclamation of 1763 is specifically referenced in section 25(a) of the Charter as a source of Indigenous rights. Modern treaties signed under section 35 (such as the Nisga'a Final Agreement of 2000 and the Tla'amin Final Agreement of 2016) have constitutional status.

The Constitution also includes unwritten conventions inherited from the British Westminster tradition. These include the convention that the Prime Minister leads the party with the most seats in the House of Commons, the confidence convention requiring the government to command majority support in the House, the responsible-government convention requiring ministers to be Members of Parliament or Senators, and the convention that the Governor General acts on the advice of the Prime Minister. The Patriation Reference (1981) and the Reference re Secession of Quebec (1998) recognised that constitutional conventions are politically (though not legally) binding.