Pierre Dubuc completed studies in political science at the Université de Montréal.
In 1996, he contributed to the creation of the Chaire d'études socio-économiques de l'UQÀM, which he directed for two years.
He joined the Parti Québécois in 2004 when the pro-union, progressive SPQ Libre was founded, with his assistance.
He declared on July 20, 2005 his intention to enter the Parti Québécois leadership election of 2005 in the name of the SPQ Libre.
His candidacy was approved unanimously by the SPQ Libre on August 15, 2005, and confirmed by the Parti Québécois on September 9, 2005.