McAvoy has won a gold medal at every junior level. He won at the 2014 World U-17 Hockey Challenge (January), 2015 IIHF World U18 Championships and 2017 World Junior Ice Hockey Championships. McAvoy led all defenseman in scoring at the 2018 IIHF World Championship, with 9 points despite only playing 6 games because the Boston Bruins were still in the second round of the NHL Stanley Cup playoffs. He won the bronze medal at the tournament.