A free agent, Giroux was invited to Gatineau Olympiques training camp for a walk-on tryout. He was signed shortly after. During his rookie season with the Olympiques, Giroux scored 39 goals for a total of 103 points in 69 games and was named Quebec Major Junior Hockey League (QMJHL)'s Rookie of the Year. He entered the 2006 NHL Entry Draft and was selected 22nd overall by the Philadelphia Flyers. The Flyers signed Giroux to an entry-level contract on July 23, 2007.