Following a memorable 1976–77 season in which he set WCHL records for defenders with 105 assists and 127 points (later broken by Cam Plante), he was selected in the first round (17th overall) in the 1977 NHL amateur draft by the Philadelphia Flyers.

The deal would prove controversial, as McCarthy was damaged goods and played only a single game for Vancouver before requiring surgery for a pre-existing hip condition.

It would be the first of four consecutive 40-point seasons on the Canuck blueline for McCarthy, who impressed with his powerful point shot and fine outlet passing and was quickly becoming the team's top all-around defender.

McCarthy responded with the finest season of his career, tying a team record for defenders with 16 goals and registering a career-high 53 points.

After another fine season in 1981–82, McCarthy would suffer a broken ankle on the eve of the 1982 playoffs, and was forced to watch from the pressbox as the Canucks marched all the way to the Stanley Cup Finals before losing to the New York Islanders.

After a poor start to the 1983–84 season, McCarthy would be a victim of a rebuilding process in Vancouver and was dealt to the Pittsburgh Penguins for a draft pick, one of three top defenders (along with Harold Snepsts and Lars Lindgren) shipped out within a few months of each other.