At the conclusion of his sophomore season, Copley opted to turn professional, agreeing to a two-year, entry-level contract with the Washington Capitals on March 20, 2014.

[1] Copley was assigned to AHL affiliate, the Hershey Bears, to begin his first full professional season in 2014–15.

[2] In the 2015–16 season, Copley made his NHL debut with the Blues in relief in a defeat to the Nashville Predators on February 27, 2016.

[11] As a free agent following the 2021–22 season, Copley signed a one-year, $850,000 contract with the Los Angeles Kings on July 13, 2022.

[14] During the 2023–24 season, Copley played in eight games before sustaining an injury during practice on December 15, 2023, and was then placed on the long-term injured reserve list two days later.