Mullen's NHL career spanned 16 seasons across four teams: the St. Louis Blues, Calgary Flames, Pittsburgh Penguins, and Boston Bruins. He established himself as a consistent offensive force, becoming the first American-born player to reach 500 goals and 1,000 points. His impressive shooting percentage and ability to contribute on both ends of the ice earned him three Stanley Cup victories: with the Flames in 1989 and the Penguins in 1991 and 1992.

Mullen was not just about scoring goals; he also displayed remarkable sportsmanship. He twice earned the Lady Byng Trophy, awarded to the player demonstrating the most gentlemanly conduct while maintaining a high level of play. This quality, coupled with his leadership and work ethic, made him a valuable asset to any team he played for.

Upon retiring in 1997, Mullen held the record for most points and goals by an American-born player, later surpassed by Mike Modano and Phil Housley, respectively. However, his impact on the game continues to be recognized. He was inducted into the United States Hockey Hall of Fame in 1998, the Hockey Hall of Fame in 2000, and the Pittsburgh Penguins Hall of Fame in recognition of his outstanding contributions to the team.

Joe Mullen's career inspires aspiring players, showcasing the power of dedication, sportsmanship, and a relentless pursuit of excellence.