Cadieux joined the Department of External Affairs in 1941,[2] served as senior adviser to Canadian members of the International Control Commission in Vietnam in 1954, and became the legal advisor to the Department of External Affairs in 1956.
Cadieux served on the negotiating committee to determine maritime boundaries with the United States.[5][1] He was Canada's first francophone Ambassador to the United States from 1970 to 1975,[6][7] and head of the Canadian Mission to the European Communities from 1975.
He was appointed to advise the Royal Canadian Mounted Police (RCMP) in 1978. He also wrote several books on Canadian diplomacy.