After the creation of the Dominion of Canada in 1867 he became leader of the Liberal opposition in the first House of Commons. One of the dominant figures of Canada’s early days of nationhood, Mackenzie defeated the Conservatives under Sir John (Alexander) Macdonald to become the country’s first Liberal Prime Minister (1873–78). During his term in office voting by ballot was introduced, the Canadian Supreme Court formed, and the territorial government of the Northwest Territories successfully organized.