He was the National Assembly of Quebec for Lac-Saint-Jean from 1976 to 2002 and occupied several portfolios as a Minister under the Parti Québecois governments of René Lévesque, Pierre-Marc Johnson, Jacques Parizeau, Lucien Bouchard and Bernard Landry.
After teaching at a local school board, he was a history teacher for nine years at Collège d'Alma before his entry to provincial politics in 1976.
He was later promoted as the Chief Whip in 1982, before being named into the Cabinet for the first time in 1984 as Minister of Recreation, Hunting and Fishing until the 1985 elections.
Despite the PQ losing the election to the Quebec Liberal Party, Brassard was re-elected in 1985 and 1989, serving as the Chief Whip of the Official Opposition.
Brassard resigned after refusing a secondary Cabinet position offered by then-Premier Bernard Landry.