Morin made his international debut in 2008 representing the United States at the IIHF World U18 Championships. In his first international tournament, he scored a team-leading six goals in seven contests. the United States defeated Sweden 6–3 in the Bronze medal game earning Morin his first international medal. Morin finished the tournament eighth overall in scoring with eight points. The following year, he again represented the United States at the 2009 IIHF World U18 Championships. Team USA defeated Russia in the final, 5–0, winning the gold medal. Morin lead the team in goal scoring, with seven and tied for second in points, with ten, his ten points ranked him tenth in tournament scoring. Morin also represented the United States at the 2010 World Junior Championships, where he registered five assists and seven points in seven games. In the tournament final, the U.S. defeated Canada 6–5 in overtime, winning gold. After being loaned from the Blackhawks so he could participate in the 2011 World Junior Championships, Morin was named an alternate captain for Team USA. During the team's first game, a 3–2 overtime win against Finland, Morin suffered what was thought to be a significant shoulder injury. However, he returned to the American lineup after missing only one game. In the tournament quarterfinals, the U.S. lost to Canada, 4–1. They rebounded in the bronze medal game defeating Sweden 4–2. The victory marked the first time Team USA won medals in back-to-back tournaments, and the first medal they won on home soil. During the tournament, Morin registered one assist through four games.