Léo Alphonse Joseph Cadieux PC (/kəˈdjuː/ kə-DEW, French: [kadjø]; May 28, 1908 – May 11, 2005) was a Canadian politician.

In 1967, he was promoted to Minister of National Defence (and the first Francophone to hold the post), and remained in that position under Pearson and then Pierre Trudeau until he retired from politics in 1970.

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 the North Atlantic Treaty Organization'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 Canadian Emergency Measures Organization, Canada's civil defence agency.