In 2017, Tomiyasu was selected the Japan U-20 national team for 2017 U-20 World Cup. At this tournament, he played all 4 matches as center back with Yuta Nakayama. On October 12, 2018, he debuted for the Japan national team against Panama. In 2019, he participated 2019 Asian Cup. He played all 7 matches and Japan won the 2nd place. He also participated 2019 Copa América.