Drafted out of the Quebec Major Junior Hockey League (QMJHL) 22nd overall in 1998, Gagné played major junior with the Beauport Harfangs and Quebec Remparts for three seasons. He began his NHL career with the Flyers in 1999 and was named to the NHL All-Rookie Team. He has appeared in two NHL All-Star Games and has won two Bobby Clarke Trophies with the Flyers as team MVP.