This is a list of ambassadors of Canada to the United States, formally titled as Ambassador Extraordinary and Plenipotentiary to the United States of America for His [Her] Majesty's Government in Canada. Originally, Canada's top diplomatic representative to the U.S. had the rank of Envoy Extraordinary and Minister Plenipotentiary. The title was promoted to the rank of Ambassador Extraordinary and Plenipotentiary in 1943, during the period when Leighton McCarthy had the post.