McAvoy played for the USA Hockey National Team Development Program in the United States Hockey League for two seasons. During the 2015–16 NCAA men's ice hockey season, BU coach David Quinn paired McAvoy with star BU defenseman and future fellow NHL player Matt Grzelcyk, already selected as a third round 2012 NHL Entry Draft pick by the Boston Bruins. McAvoy was part of the gold medal-winning team at the 2015 IIHF World U18 Championships. He was also a member of the bronze medal-winning U-20 team at the 2016 World Junior Ice Hockey Championships.