[2][3] Leonard represented the United States at the 2022 IIHF World U18 Championships where he recorded five goals and one assist in six games and won a silver medal.

He scored the game-winning goal in overtime of the championship game against Sweden to help team USA win a gold medal.

[6] He again represented the United States at the 2025 World Junior Ice Hockey Championships, where he served as team captain and recorded five goals and five assists in seven games and won a gold medal.

He was subsequently named the inaugural Murray Costello World Junior Championship MVP award winner.

[7] He helped team USA win back-to-back gold medals at the IIHF World Junior Championship for the first time in history.