As a youth, Gauthier played in the 2008 Quebec International Pee-Wee Hockey Tournament with the Montreal Canadiens minor ice hockey team.[3] He played alongside Anthony Duclair, although they were eventually eliminated by a team with Jonathan Drouin on its roster.[4] Gauthier eventually advanced to the Collège Esther-Blondin Phénix in midget AAA[5] and led the team to the 2012 Telus Cup.[6] During the tournament, he recorded two goals and nine assist in seven games.[7] As a teenager attending Académie Antoine-Manseau, Gauthier played quarterback on their football team in addition to hockey.[8] He was eventually drafted by the Rimouski Océanic of the Quebec Major Junior Hockey League (QMJHL) during the 2011 QMJHL Entry Draft,[7] although he intended to study at Harvard University and play for their Division 1 ice hockey team.[9] In spite of this, Penguins captain Sidney Crosby, who was an Océanic alumni, convinced Gauthier to play junior ice hockey with Rimouski Océanic in the QMJHL.[9] Gauthier also turned down the opportunity to play in the United States Hockey League with the Youngstown Phantoms.[8]