Justin Carbonneau was born in Levis, QC, Canada and started for the Pointe-Levy Corsaires Bantam AAA team as a 13-year-old. In 2021-2022, he played for the Levis Chevaliers of the QM18AAA league and tallied eight goals and 32 assists in 40 games. Charbonneau was much more productive during the 2022-2023 season when he played in 23 games for Levis Chevaliers and registered 15 goals and 14 assists. He also played in the QMJHL between Rouyn-Noranda Huskies and the Blainville-Boisbriand Armada. He played 32 games in the QMJHL and tallied five goals and 15 assists.
Carbonneau got his first taste of International play in 2022-2023, he tallied one assist in six games for Canada White U17 in the WHC-17 tournament.
In 2023-2024, Carbonneau had the type of season that helped his draft stock out. Playing for Blainville-Boisbriand of the QMJHL, he tallied 22 goals and 23 assists in just 31 games.