Rielly represents Canada internationally. He started out in regional and age-group competitions. When he was representing Team Pacific at the 2011 World U-17 Hockey Challenge, Rielly scored two goals in five games and helped his team capture a bronze medal. Later that year, Rielly was part of Canada's gold medal winning squad at the 2011 Ivan Hlinka Memorial Tournament. Rielly's first experience at an International Ice Hockey Federation sanctioned event was the 2011 IIHF World U18 Championships, where he recorded two goals and one assist in seven games. Canada finished fourth at the tournament.