Thierry St-Cyr (born November 7, 1977) is an engineer and former Bloc Québécois politician in Quebec, Canada.

He was actively involved with the Université de Sherbrooke, serving as president, administrator and honorary member of its engineering student association, president of Le Collectif, the school's campus newspaper, and board member of the school's faculty of engineering in 2000 and 2001.

He has worked as a quality and metric control at Motorola in Montreal from 2001 until 2006 when he entered politics.

St-Cyr ran for the Bloc in the 2004 election in Jeanne-Le Ber, where he lost to Liza Frulla of the Liberal Party of Canada by 72 votes.

He served as vice-chair of the standing committee on citizenship and immigration, and its subcommittee on agenda and procedure.