Involved in politics since 1979, St-Jacques first stood for office in the 1997 federal election as the Progressive Conservative candidate for Shefford.
With Sherbrooke's Jean Charest as a national leader, the party experienced a resurgence in Quebec's Eastern Townships, and St-Jacques was elected to the House of Commons, taking her seat from the Bloc Québécois.
Until she left the PC caucus, she was its designated parliamentary critic for International Cooperation, La Francophonie, and children and youth.
"[citation needed] In 1999, St-Jacques joined MPs Svend Robinson (NDP) and Réal Ménard (Bloc), both openly gay, and Toronto Liberal MP Bill Graham, in a "pink caucus" across party lines.
The social conservative Campaign Life Coalition decried St.-Jacques as "a married mother of one, who says she isn't a lesbian but who supports the gay agenda.