Drafted out of Regina of the WCHL after leading them to a Memorial Cup championship the previous season, the Alberta native spent his entire rookie season with the Capitals in their inaugural season if 1974-75. Hampered by a knee injury midway through the season, Joly appeared in only 44 games, recording one goal and seven assists, and posted a plus/minus rating of minus-68.
With his first professional season behind him, Joly began the 1975-76 season with Richmond of the AHL but was recalled by the Capitals after only three games. Although the Capitals were unable to improve much in their second season - winning 11 games as opposed to eight - Joly, only 22, showed some progress. In 54 games, he led team defenseman in scoring with eight goals and 17 assists. However, being a number-one overall pick, the expectations that Joly would become the young team's franchise player were beginning to fall flat.
After beginning the 1976-77 with Springfield of the AHL, the Capitals, in desperate need of veteran leadership and running out of patience, traded Joly to Detroit in exchange for Bryan Watson in November 1976.
Joly appeared in 276 games over seven seasons with Detroit following his departure from Washington and retired from professional hockey at 31. Like many before and after him, Joly never did live up to the expectations and pressure of being a number-one draft pick.
