[2] After playing two-plus seasons with the Tigres, during which he scored 56 goals, Gagné was traded in December 2015 to the Shawinigan Cataractes in exchange for James Phelan and a draft pick.

In the final year of his entry-level contract in the 2018–19 season, Gagné contributed with 9 points in 33 games with AHL affiliate, the Belleville Senators, before he was traded by Ottawa to the Toronto Maple Leafs in exchange for Morgan Klimchuk on January 11, 2019.

[6][7] As the Americans' offensive leader, Gagné collected 26 points in 25 games before signing a professional tryout with the Ontario Reign of the AHL on December 18, 2019.

[8] He returned to the Americans after 3 games, and continued to lead the ECHL with 24 goals before agreeing to his second PTO in the AHL with the Rockford IceHogs, affiliate to the Chicago Blackhawks on January 18, 2020.

[9] Finding a role within the IceHogs, contributing with 11 points through 19 games, Gagné was signed to an AHL contract for the remainder of the season on March 7, 2020.