The Honourable Léo Alphonse Joseph Cadieux (born May 28 1908, Saint-Jérôme, Quebec) is a former Canadian politician.

A newspaper journalist and publisher, Cadieux was first elected to the Canadian House of Commons as the Liberal Member of Parliament for Quebec, Quebec in the 1962 Canadian election. In 1965, he was appointed to the Cabinet by Lester Pearson as Associate Minister of Natioanl Defence. In 1967 he was promoted to Minister of National Defence and remained in that position under Pearson and then Pierre Trudeau until he retired from politics in 1970 to become Canada's Ambassador to France. He remained Canada's envoy to Paris until 1975.

During Cadieux's tenure as Defence minister, Canada cut its troop commitment to Europe from 10,000 to 5,000 troops and ended Canada's commitment to send re-enforcements to NATO's Central Front following a review of Canadian defence priorities. In Cabinet debates on Canada's attitude towards nuclear deterrence, Cadieux argued in support of the doctrine. He also oversaw the reorganization of the Candian Emergency Measures Oragnizations, Canada's civil defence agency.

In 1974 he was made an Officer of the Order of Canada.