The Right Honourable Ian Alistair Mackenzie (July 27, 1890 - September 2, 1949) was a Canadian parliamentarian.

Mackenzie entered politics by winning a seat in British Columbia's legislative assembly in 1920. In 1930 he was appointed to Prime Minister William Lyon Mackenzie King's pre-election Cabinet as Minister of Immigration and Colonization and Superintendent of Indian Affairs but while he won his seat in the 1930 federal election the Liberals were defeated across the country and Mackenzie entered Parliament as an Opposition MP.

When the Liberals returned to power through the 1935 Canadian election, Mackenzie returned to Cabinet as Minister of National Defence where he had the responsibility for pre-war rearmament. With the outbreak of World War II in 1939, however, Mackenzie was moved to the position of Minister of Pensions and National Health, in part because of his role in a scandal involving the awarding of a contract to manufacture the Bren Gun. In 1944 he became Minister of Veterans Affairs.

Mackenzie was an able parliamentarian and when the increasing pressures of war led Prime Minister King to decide to delegate some of his responsibilities in the House of Commons to the new position of Government House Leader he chose Mackenzie as the first MP to hold that responsibility.

During the war, Mackenzie pandered to anti-Japanese sentiment in British Columbia by declaring to his constituents at his 1944 nomination meeting "Let our slogan be for British Columbia: 'No Japs from the Rockies to the seas.'" As British Columbia's senior cabinet minister Mackenzie had had a key role in the government's decision to intern Japanese-Canadians for the duration of the war.

In 1947, Mackenzie was named to the Imperial Privy Council along with several other senior Canadian Cabinet ministers allowing him to use the honorific of Right Honourable. In 1948 he was elevated to the Canadian Senate but served only a year and a half until his death in 1949.