With the Millionaires, he broke the scoring record with 76 goals and 92 assists for 168 points in 57 games,[1] playing on a line with Kelly Dean and Dwaine Turberfield.

He then moved on to the Brandon Wheat Kings of the WHL, a team that featured future NHL players Brad McCrimmon, Bill Derlago, Laurie Boschman, Dave Semenko, Glen Hanlon, Ray Allison, and Walt Poddubny.

In the 1980 playoffs, he led the all-rookie left wingers in goals (5), assists (10), and points (15), which the Flyers lost in Game 6 of the Stanley Cup Finals.

Finally, with 1:37 left in regulation in Game 6, Flyer goaltender Ron Hextall took matters into his own hands, slamming Chelios into the boards and pummeling him with blows, apparently in retaliation for the hit on Propp.

In all of the major categories in the regular season and playoffs, he has made the top 3 among left wingers a remarkable 29 times in that decade.

Propp, who was a pending free agent unlikely to return to Philadelphia the next season, appreciated former teammate Clarke sending him to a top team.

"[4] The Bruins continued their success in the post-season and made a run to the Stanley Cup Finals where they ultimately fell to the Edmonton Oilers.

Propp enjoyed an excellent debut season in Minnesota, scoring 73 points and helping the team to an improbable run to the Stanley Cup Finals, where they lost to the Pittsburgh Penguins.

Propp moved past Bobby Hull on the all-time playoff scoring list among left wingers to become the highest-scoring left winger in NHL playoff history on April 12, 1991 as the North Stars beat the Chicago Blackhawks 6–0 in Game 5 in the series, with Propp leading the charge by scoring first on Dominik Hasek.

After the lockout, however, Propp did not return to play in the National Hockey League, nor did he continue his career in Europe opting instead to retire from the game.

Propp holds a hapless achievement in that he went to the Stanley Cup Finals five times, with Philadelphia in 1980, 1985, and 1987, with the Boston Bruins in 1990, and with Minnesota in 1991, without ever winning.

Propp finished with 1,004 points over 1,016 NHL games in 15 NHL seasons, and ranks second in Flyers history in goals (369, behind Bill Barber), third in assists (480, behind Bobby Clarke and Claude Giroux), and fourth overall in games played in a Flyers uniform (behind Barber, Clarke, and Giroux).

In 1999, Propp was named to the MasterCard Canadian Junior All-Time team, which also included Mario Lemieux, Guy Lafleur, Bobby Orr, Denis Potvin, and Bernie Parent.