After being a late cut from Team Canada's 2018 IIHF World Junior Championship roster, DiPietro eventually made his World Juniors debut during the 2019 IIHF World Junior Championships. In the first game of the tournament on December 26, 2018, DiPietro recorded a shut-out in a 14–0 win over Denmark. In Canada's final game of the preliminary round, DiPietro was named Canada's best player of the game in a 2–1 loss to Russia. He ended the preliminary round with a .957 save percentage. On January 2, Canada was eliminated from the World Juniors tournament in a heartbreaking 2–1 overtime loss in the quarterfinals to Team Finland.