Mullen played junior ice hockey for the Sioux Falls Stampede in the United States Hockey League (USHL) during the 2004–05 season.
He registered 37 points in 60 games, fourth on the team; he also led the Stampede in plus-minus with a +11 rating.
After the season, Mullen chose to attend the University of Denver (DU) in part for the coaches and the city of Denver.

Prior to his first season with the Pioneers, Mullen was named Preseason Player to Watch by College Hockey News.
He scored his first career goal in a 4–2 win against the Air Force Academy, helping DU to their first win of the year.
He finished the year with 7 goals and 17 points in 37 games, tying for sixth on the team for goals and points.
The following season, he recorded four multi-point games, though he only managed to duplicate the 17 points recorded in his freshman season.
Mullen spent most of the season on forward, but also played four games as a defenseman.
He missed the Western Collegiate Hockey Association (WCHA) playoffs after contracting mononucleosis.
Following the conclusion of the season, Mullen was named to the All-WCHA Academic Team.

In the 2007–08 season, Mullen began the year playing defense.
Though he did spend some time at forward, Mullen led all DU defenders in scoring by season's end.
In back-to-back games leading up to the WCHA playoffs, Mullen received two 10-minute misconduct penalties.
As a result, head coach George Gwozdecky suspended Mullen for the first game of the playoffs.
Mullen returned from his suspension the following game and helped the Pioneers to an eventual WCHA tournament win.
In his senior season, Mullen set career highs in assists and points while leading Denver in blocked shots.
At the conclusion of the year, he was again named to the All-WCHA Academic Team and was awarded the Lowe's Senior CLASS Award.

Undrafted out of college, Mullen signed a two-year entry-level free agent contract with the Los Angeles Kings on April 3, 2009.
Playing with the Kings farm team the Manchester Monarchs, Mullen recorded his first professional point, an assist, in his first game, a 6–3 victory over the Albany River Rats.
His first professional goal came almost two months later in a 4–2 win against the Springfield Falcons.
After playing 36 games for the Monarchs, Mullen was sent down to their ECHL affiliate, the Ontario Reign.
After playing only one game for the Reign, he was recalled by Manchester.
He finished the year playing 8 more games for the Monarchs bring his total to 44 and recorded 4 goals and 10 points in his first professional season.
In the playoffs Mullen played two games without recording a point.
 In his second season Mullen received more responsibilities after being added to the Monarchs power play unit, and while he played mostly on defense, he did see some ice time at forward.
With the changes he doubled his production to 20 points in 67 games.
During the off-season Mullen was re-signed by the Kings to a one-year contract.
In his third season he again double his point production registering 41 points in 69 games.
He also played in 4 playoff games for the Monarchs registering a goal and three points.

Following the completion of his contract Mullen left the Kings organization as a free agent and signed with the Vancouver Canucks.
Due to the depth on defense on Vancouver Mullen was not expected to make the Canucks out of training camp.
With the 2012–13 lockout approaching Mullen was assigned to the Canuck's American Hockey League affiliate, the Chicago Wolves.
In his second game with the Wolves Mullen suffered an injury to his left shoulder.
The injury required surgery which ended his season.
Despite his limited playing time in Chicago the Canucks re-signed Mullen to a one-year contract in the off-season.

On March 4, 2014, Mullen was traded by the Canucks to the Ottawa Senators organization for Jeff Costello.

In the 2015–16 season, his third within the Senators' organization, Mullen was traded by Ottawa to the Nashville Predators in exchange for Conor Allen on January 14, 2016.

At the conclusion of the season and out of contr
Mullen played junior ice hockey for the Sioux Falls Stampede in the United States Hockey League (USHL) during the 2004–05 season. He registered 37 points in 60 games, fourth on the team; he also led the Stampede in plus-minus with a +11 rating. After the season, Mullen chose to attend the University of Denver (DU) in part for the coaches and the city of Denver.
Prior to his first season with the Pioneers, Mullen was named Preseason Player to Watch by College Hockey News. He scored his first career goal in a 4–2 win against the Air Force Academy, helping DU to their first win of the year. He finished the year with 7 goals and 17 points in 37 games, tying for sixth on the team for goals and points. The following season, he recorded four multi-point games, though he only managed to duplicate the 17 points recorded in his freshman season. Mullen spent most of the season on forward, but also played four games as a defenseman. He missed the Western Collegiate Hockey Association (WCHA) playoffs after contracting mononucleosis. Following the conclusion of the season, Mullen was named to the All-WCHA Academic Team.
In the 2007–08 season, Mullen began the year playing defense. Though he did spend some time at forward, Mullen led all DU defenders in scoring by season's end. In back-to-back games leading up to the WCHA playoffs, Mullen received two 10-minute misconduct penalties. As a result, head coach George Gwozdecky suspended Mullen for the first game of the playoffs. Mullen returned from his suspension the following game and helped the Pioneers to an eventual WCHA tournament win. In his senior season, Mullen set career highs in assists and points while leading Denver in blocked shots. At the conclusion of the year, he was again named to the All-WCHA Academic Team and was awarded the Lowe's Senior CLASS Award. 
Undrafted out of college, Mullen signed a two-year entry-level free agent contract with the Los Angeles Kings on April 3, 2009. Playing with the Kings farm team the Manchester Monarchs, Mullen recorded his first professional point, an assist, in his first game, a 6–3 victory over the Albany River Rats. His first professional goal came almost two months later in a 4–2 win against the Springfield Falcons. After playing 36 games for the Monarchs, Mullen was sent down to their ECHL affiliate, the Ontario Reign. After playing only one game for the Reign, he was recalled by Manchester. He finished the year playing 8 more games for the Monarchs bring his total to 44 and recorded 4 goals and 10 points in his first professional season. In the playoffs Mullen played two games without recording a point.  In his second season Mullen received more responsibilities after being added to the Monarchs power play unit, and while he played mostly on defense, he did see some ice time at forward. With the changes he doubled his production to 20 points in 67 games. During the off-season Mullen was re-signed by the Kings to a one-year contract. In his third season he again double his point production registering 41 points in 69 games. He also played in 4 playoff games for the Monarchs registering a goal and three points.
Following the completion of his contract Mullen left the Kings organization as a free agent and signed with the Vancouver Canucks. Due to the depth on defense on Vancouver Mullen was not expected to make the Canucks out of training camp. With the 2012–13 lockout approaching Mullen was assigned to the Canuck's American Hockey League affiliate, the Chicago Wolves. In his second game with the Wolves Mullen suffered an injury to his left shoulder. The injury required surgery which ended his season. Despite his limited playing time in Chicago the Canucks re-signed Mullen to a one-year contract in the off-season.
On March 4, 2014, Mullen was traded by the Canucks to the Ottawa Senators organization for Jeff Costello.
In the 2015–16 season, his third within the Senators' organization, Mullen was traded by Ottawa to the Nashville Predators in exchange for Conor Allen on January 14, 2016.
At the conclusion of the season and out of contr
Patrick Mullen (ice hockey)