Legault was a member of the National Assembly of Quebec from 1998 to 2009. During this time, he was a part of the Parti Québécois (PQ). He was a cabinet minister while Lucien Bouchard and Bernard Landry were Premier. He was elected in the 1998, 2003, 2007, and 2008 elections. He did not run for election again in 2009, and stopped being a member of the National Assembly that year. As a part of the CAQ, he became a member of the National Assembly again after the 2012 provincial election.