On January 5, 2021, Zegras, representing the United States at the 2021 IIHF World Junior Championships won the gold medal over Canada 2–0, and scored 1 goal and recorded 1 assist during the game. He was named World Juniors MVP after scoring 7 goals and recording 11 assists during the tournament, which he also led in scoring. He also tied the Team USA points record held by Jordan Schroeder.