Born in Montreal, Quebec, Dupuis has a law degree from the Université de Montréal and was named to the Barreau du Québec in 1974. and is a former lawyer.

He was also a designated teacher in Halifax, Nova Scotia a chief of staff for the Ministry of Workforce, Income Security and vocational training and for the Quebec Liberal Party and an Attorney General.

He was also the vice-president of Association of Criminal Defence Lawyers of Montreal and a member of the Administrative Law Society.

He was re-elected in 2007, and was renamed the Minister of Public Security and was added the portfolio of Justice but was no longer the Government House Leader and Deputy Premier, positions that were given to Jean-Marc Fournier and Nathalie Normandeau respectively.

On June 23, 2009, Dupuis gave up on request the portfolio of Canadian Intergovernmental Affairs to Claude Bechard during a cabinet shuffle.