Petit began his career at minor club ES Arques-la-Bataille before being signed by Arsène Wenger's Monaco side at the age of 18. He made his debut soon after and played in the 1989 Coupe de France final. Petit became a regular at Monaco, playing as a left-sided or central midfielder. In 1991, he won the Coupe de France with Monaco and also played in the 1992 European Cup Winners' Cup final (which Monaco lost to Werder Bremen). In 1996–97, his final season at Monaco, he captained his side to the Ligue 1 title.