Petit specialized in labour and administrative law and has organized for the Conservatives and the Progressive Conservatives since the 1980s.
He was first elected to the House of Commons of Canada in the 2006 federal election as the Conservative Member of Parliament for Charlesbourg—Haute-Saint-Charles.
In the 2011 election, he was defeated by Anne-Marie Day of the NDP.
He currently serves as the legal commission president of the Conservative Party of Quebec.