He subsequently entered politics and was defeated in his attempt to win a seat in the Canadian House of Commons in the 1988 election. He was elected on his second attempt in the 1993 election as the Liberal Member of Parliament for Laval West. He immediately joined the Cabinet, serving concurrently as Minister of Communications and Minister of Multiculturalism and Citizenship from 1993 until January 1996. During his tenure, the departments he oversaw were merged into the new Department of Canadian Heritage
Dupuy came under fire for "representing a constituency in a Canadian Radio-television and Telecommunications Commission (CRTC) application" because he was the minister responsible for the agency, and was subsequently dropped from Cabinet.
He did not run in the 1997 election.