He turned pro the following season, and spent the first half of the year with the Seals' Central Hockey League farm team in Salt Lake, but was dealt to the St. Louis Blues before he ever played a game in California.

In 1975–76, Affleck made the Blues' squad full-time and was a huge success as a mobile, puck-moving defender.

However, by 1977–78 he was struggling, as he slumped to 18 points and a -56 rating on a St. Louis team which finished with just 20 wins and missed the playoffs.

He returned to Indianapolis full-time for the 1983–84 season, and was named the league's top defender for the third time along with MVP honours.

Affleck finished his NHL career with 14 goals and 80 points, along with 86 penalty minutes, in 280 games.