Cormier was drafted 68th overall by the Golden Knights in the third round of the 2020 NHL entry draft, signing his three-year entry-level contract on December 31, 2020,[1] and played junior hockey with the Charlottetown Islanders of the QMJHL. Cormier experienced a breakout season in 2020–21 season, winning the Emile Bouchard Trophy as the league's best defenseman,[2] and being named to the season's First All-Star Team. Cormier repeated both feats in 2021–22 season,[3] additionally leading the league in both goals and points by a defenseman, and helping the Islanders to the President's Cup Finals, where they ultimately lost to the Shawinigan Cataractes.
Cormier made his NHL debut with Vegas on January 6, 2024, recording an assist on a third-period Jack Eichel power-play goal for his first NHL point.[4]