Bouchard experienced championship success early in his junior hockey career when he helped London win the 2016 Ontario Hockey League championship and Memorial Cup in his first full season with the Knights, who chose him with the No. 17 pick in the 2015 OHL Priority Selection. He was named captain for the 2017-18 season, which he ended as a finalist for the Max Kaminsky Trophy as Defenseman of the Year and the Red Tilson Trophy as MVP of the OHL.
The Oilers selected Bouchard with the No. 10 pick in the 2018 NHL Draft and signed him to a three-year, entry-level contract on July 17, 2018. He became the youngest defenseman in Oilers history to score a goal in a 4-1 win against the Washington Capitals on Oct. 25 after turning 19 five days before the game. He was returned to London on Nov. 2 after playing seven NHL games. He had 53 points (16 goals, 37 assists) and 21 (four goals, 17 assists) in 11 playoff games for the Knights and won the Max Kaminsky Trophy as the league's top defenseman.