Harley earned his first career point, an assist on a goal by Albert Michnac, in a 4–3 loss to the Saginaw Spirit on October 15.

Harley recorded his first OHL career multi-point game on February 23, earning two assists in a 4–0 win over the Niagara IceDogs.

One week later, on March 29, Harley recorded his first career playoff point, assisting on a goal scored by Cole Carter in a 5–4 loss to the Colts.

On December 31, Harley recorded his first multi-goal game of his OHL career, as he scored two goals against the Windsor Spitfires in a 9–5 victory.

On March 22, Harley recorded his first career multi-point playoff game, earning two assists in a 5–2 loss to the Sudbury Wolves.

[1] At the end of the season, Harley was named the winner of the Bobby Smith Trophy as the OHL Scholastic Player of the Year.

[13] Following the draft, Harley attended the Steelheads training camp before playing in the Traverse City annual rookie tournament.

[14] Harley then attended the Stars' training camp, where he drew comparisons to Dallas defenceman Miro Heiskanen from head coach Jim Montgomery.

[15] During preseason games, Harley had opportunities to play alongside Heiskanen and veteran John Klingberg while averaging over 20 minutes of ice time.

[16] When the NHL resumed play for the 2020 Stanley Cup playoffs, Harley was named to the Stars' taxi squad and stayed with them in the Edmonton bubble.

[19] During the two months between his last Steelheads game and the taxi squad, Harley added 10 pounds of muscle due to working out consistently.

[17] He remained on the team's taxi squad until John Klingberg and Taylor Fedun were deemed unfit to play in the Stars' Western Conference seeding round-robin game against the Colorado Avalanche.

[27] Harley returned to the Dallas Stars training camp ahead of the 2021–22 NHL season but was again reassigned to the AHL before the final roster was announced.

[28] Despite struggling at the start of the season, Harley was recalled to the NHL level on November 1 after playing in six AHL games and recording one point.

[29] Although the team had a sufficient number of forwards and defensemen, head coach Rick Bowness stated that he brought Harley in to "bring an element which could help the Stars create more goals.

However, following a trade for Nils Lundkvist and an unimpressive training camp, Harley spent the majority of the 2022–23 season in the AHL with the Texas Stars.

[39] Upon joining the Stars in the AHL, Harley was removed from teams' power-play unit for their first six games in order for him to focus more on his defensive capabilities.

[43] After participating in the Dallas Stars' development camp and preseason games, Harley was named to their opening night roster ahead of the 2023–24 season.

[52] Harley returned to Team Canada's selection camp the following year and was named to the final roster to compete at the 2021 World Junior Ice Hockey Championships.