Lachapelle served in the National Assembly of Quebec from 1981 to 1985, representing the Montreal riding of Dorion as a member of the Parti Québécois (PQ).
She was a graduate of the Elie Business College à Montréal and was a parliamentary aide for PQ cabinet minister Lise Payette from 1976 to 1981.
[2][3][4] Lévesque resigned as PQ leader and premier in 1985, and Lachapelle supported Pierre-Marc Johnson's successful bid to succeed him.
[5] When asked about rival candidate Pauline Marois's prospects of winning, Lachapelle responded that she did not believe Quebecers were ready for a woman to be premier.
[6][7][8] Lachapelle was defeated in the 1985 provincial election, losing by a narrow margin to Liberal candidate Violette Trépanier.