Born in a working class family, Marois studied social work at Université Laval, married businessman Claude Blanchet and became an activist in grassroots organizations and in the Parti Québécois (a social democratic party advocating Quebec's independence) [REF].
After being defeated as a PQ candidate in La Peltrie in the 1985 general election and in a by-election in 1988, she was elected as the member of the Quebec National Assembly for Taillon in the 1989 general election.