 In the off-season, Copley was included in a trade, which also included Troy Brouwer and a third-round pick in 2016, to the St. Louis Blues in exchange for T. J. Oshie on July 2, 2015.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.During the 2016–17 season, on January 20, 2017, Copley was recalled from the Chicago Wolves of the AHL by the Blues.