Thériault was born in
Montreal. He attended
Université du Québec à Montréal, earning a bachelor's degree in philosophy in 1984 and a Masters in political philosophy in 1988. He later earned a
DESS in
bioethics at the
Université de Montréal in 2002. After obtaining his master's degree, he taught philosophy at
Collège de Maisonneuve from 1985 to 2003. He also coached
water polo from 1979 to 1988. He served as a member of the Ethics Committee of the Maisonneuve-Rosemont Hospital and Jeanne-Le Ber nursing home from 2000 to 2003. He was a member of the Board of Directors of the Maisonneuve Cooperative School (Coopérative scolaire Maisonneuve) from 2001 to 2003. He was bureau chief for Parti Québécois in
Ville-Marie, Montreal from 1999 to 2003. He was elected in the
2003 Quebec general election, succeeding
Gilles Labbé. He was defeated in the
2007 Quebec general election by
Ginette Grandmont. He was elected as the vice-chair of the
Canadian House of Commons Standing Committee on Access to Information, Privacy and Ethics and the
Canadian House of Commons Standing Committee on Health in the
45th Canadian Parliament. ==Electoral record==