In February 2015, Auger-Aliassime won his first ITF junior singles title at the G3 in Querétaro. A week later, he won his second straight ITF junior singles title and first doubles title at the G4 in Zapopan. In late August 2015, he won his first junior G1 title with a victory over compatriot Denis Shapovalov in College Park. At the US Open in September 2015, his first junior Grand Slam, he reached the second round in singles and won the doubles title with Shapovalov. In October 2015, Auger-Aliassime and compatriots Denis Shapovalov and Benjamin Sigouin won the Junior Davis Cup title, the first time in history for Canada. In December 2015 at the Eddie Herr International Tennis Championship, he won his second G1 singles title after defeating Alex De Minaur in the final. At the junior event of the French Open in June 2016, he reached his first Grand Slam singles final where he was defeated by Geoffrey Blancaneaux in three sets, despite holding a championship point. In July 2016 at Wimbledon, Auger-Aliassime advanced to the quarterfinals in singles and to the final in doubles with Denis Shapovalov. At the US Open in September 2016, he won the boys' singles title with a straight-sets victory over Miomir Kecmanović. He reached the doubles final as well, with fellow Canadian Benjamin Sigouin.
