On December 25, 2018, Comtois was named captain for Team Canada's national junior team while they compete at the 2019 World Junior Ice Hockey Championships. He is the only player to return from the 2018 gold medal winning team. On December 26, Comtois scored four goals in a 14–0 win over Denmark in the first game of the tournament. Comtois became the fifth player from Team Canada to score four goals in a World Juniors game, with the last being Taylor Raddysh in 2017. After Canada was eliminated from the tournament, Comtois revealed he had been playing with a separated shoulder.