Moving up to the U20 level, Reinhart earned a spot with the national junior team for the 2014 World Junior Championships. His brother Griffin also made the team, and they became the third pair of brothers to play for Canada at the World Junior Championships. Reinhart and Aaron Ekblad were the only two players on the Canadian roster eligible for the 2014 NHL Entry Draft. Reinhart registered two goals and three assists in the first three games of the tournament, but was held scoreless for the remainder of the tournament. Canada lost the bronze medal game against Russia 2–1 and finished fourth. Sam Reinhart also represented Team Canada at the 2015 World Junior Ice Hockey Championship. The team won gold as Sam served as one of two alternate captains for the team, the other being Connor McDavid. Reinhart scored the game-winning goal against team Russia in the Gold Medal game, which was his fifth of the tournament. Reinhart finished with a total of 5 goals and 11 points leading all players in goals and points.