In December 2019, he was named to Team Canada's 2020 World Junior Ice Hockey Championships roster. After a four-point performance in the team's 6–4 win against the United States in the tournament opener, Lafrenière suffered a lower-body injury the following game after colliding with Russian goaltender Amir Miftakhov on a scoring chance in the second period. He would miss two games, and came back strong, helping lead Canada to a gold medal. He was named one of the three best players on Team Canada, tournament MVP, and was named to the media all star team. He registered four goals and six assists for 10 points in five games.