He taught international and constitutional law at Université de Montréal from 1958 until 1973.

[1] From 1966 to 1969, he chaired the Estates General of French Canada and joined in 1970 the Quebec sovereignty movement.

Since the party leader, René Lévesque, had not won a seat in the 1973 election, Morin became leader of the Opposition in the National Assembly until the 1976 election, which the Parti québécois won.

As a member of Lévesque's government, Morin was appointed successively Minister of Education (1976–1981), Cultural and Scientific Development (1981–1982) and Intergovernmental Affairs (1982–1984).

Morin returned to teaching in 1984 at Université de Montréal, where he became professor emeritus in 1997.