College Boston College offered Mullen a partial scholarship for the 1975–76 season to attend and play for the
Eagles hockey program. He paid $700 out of his own pocket in the first year, but after scoring 34 points in 24 games as a freshman, the school gave him a full scholarship. Including tournament games, he led the Eagles in goals the following three seasons with 39, 38 and 30 respectively, and points in 1977–78 with 68 and in 1978–79 with 56. Mullen led the Eagles to the
Eastern College Athletic Conference (ECAC) championship in 1977–78, and was named an all-star of the
1978 National Collegiate Athletic Association (NCAA) tournament. He scored a goal in the championship game, but the Eagles lost to cross-town rival
Boston University, 5–3. In four seasons with Boston College, Mullen set school records of 110 goals and 212 points (both subsequently broken). He was named to the All-ECAC, All-New England and NCAA All-American teams in 1978 and 1979. He won the
Walter Brown Award in 1978 as the top American-born player in New England, Boston College has twice honored Mullen; He was inducted into the school's Varsity Club Hall of Fame in 1998, while the hockey program retired his jersey number 21 the following year.
St. Louis Blues While Mullen had a successful college career, he went
undrafted by any
National Hockey League (NHL) team. However, he received interest as a
free agent from several teams following graduation as well as the
United States Olympic Team. He was named to the first all-star team and won the CHL's Most Valuable Player Award. He again reached the 40-goal plateau in
1984–85, and had 92 points total. On February 1, 1986, the Blues dealt him to the
Calgary Flames as part of a six player trade. Mullen went to Calgary, along with
Terry Johnson and
Rik Wilson, for
Eddy Beers,
Charlie Bourgeois and
Gino Cavallini.
Calgary Flames The Flames felt they needed a quality offensive player and expected Mullen to fulfill that role. He then led the league with 12 goals in the
1986 Stanley Cup playoffs. He led the
1989 Stanley Cup playoffs with 16 goals as the Flames defeated the Canadiens to win their first
Stanley Cup championship. He was sent to the
Pittsburgh Penguins in a
draft day trade on June 16, 1990, in exchange for Pittsburgh's second round selection (26th overall, which turned out to be defenseman Nicolas Perreault).
Pittsburgh and Boston The move to Pittsburgh brought Mullen closer to his New York home and fulfilled his desire to raise his family in his native United States. He also appreciated that the Penguins felt he could aid their team. Penguins' head coach
Bob Johnson, who had previously coached him in Calgary, influenced the team's decision to acquire him. an injury for which he could not identify a specific
check or incident as the cause. He returned for the third game of the Penguins' Division semifinals series against the
New Jersey Devils, scoring a goal. Mullen finished the
1991 Stanley Cup playoffs with eight goals, including two in game six of the
Final, an 8–0 victory over the Minnesota North Stars that clinched Pittsburgh's first Stanley Cup. He appeared in only nine playoff games, however, as he suffered a knee injury that required surgery to repair in the second game of Pittsburgh's Division Final series against the New York Rangers. Mullen watched from the sidelines as the Penguins repeated as Stanley Cup champions. A 38-goal season in
1993–94 led to Mullen's
third All-Star Game appearance. The game was a homecoming of sorts for Mullen, as it was played in Madison Square Garden. In the
lockout-shortened 1994–95 season, Mullen scored 37 points in 45 games. He left the Penguins following the season, signing a one-year contract as a free agent with the
Boston Bruins. Mullen chose to wear number 11 with the Bruins as his usual number 7 had been retired by the Bruins in honor of
Phil Esposito. He missed the majority of the season after requiring surgery for another herniated disc, then suffering a sprained
medial collateral ligament. He appeared in only 37 games, scoring 15 points. He appeared in 54 games and scored 22 points. He retired as a player following the season. Since his retirement Mullen has continued to play in amateur / charity games as a member of the
Boston Bruins Alumni team.
International Mullen made his first appearance with the United States National Team following his graduation from Boston College. He was a member of three
Canada Cup teams, appearing at the
1984,
1987 and
1991 tournaments. The Americans settled for second place, however, after losing to
Canada in the championship series. The United States had a disastrous 12th-place finish in the
1998 tournament, requiring them to go into a qualifying round to avoid relegation to the B division for 1999. As the qualifying tournament was played in November, American NHL players were not available. ==Playing style==