In 2007, Mulhern made his professional debut at a Gladiator Challenge event. He fought and defeated Randy Blackwell midway through the first round via submission. His next two fights were both under the King ofthe Cage banner, both fight were wins for Mulhern, one submission and one close split decision. After earning a record of 7-0, Mulhern took on the much more experienced, Chris Brennan. Mulhern dominated the fight and won via first round submission using the rare omoplata maneuver. The win earned him a title fight against current UFC fighter, Mike Guymon. The fight was back and forth but late in the fourth round, Guymon defeated Mulhern via TKO, retaining his title. Mulhern bounced back from his loss to Guymon by defeating Ultimate Fighting Championship veteran Rich Clementi at King of the Cage: Vengeance on February 12, 2010. This bout was a part of King of the Cage's debut on HDNet. Mulhern captured the King of the Cage Welterweight Championship on March 26, 2010 by defeating Koffi Adzitso at King of the Cage: Legacy. He most recently defeated Joey Gorczynski at King of the Cage: Honor. Mulhern defended his title for the first time against Levi Stout, defeating Stout via first-round submission. On December 4, 2010, Mulhern defeated the Canadian King of the Cage Welterweight Champion Garret Davis in a unanimous decision at King of the Cage: Black Ops. This event unified the Canadian King of the Cage and World King of the Cage Welterweight Championships.
Strikeforce
On May 6, 2011, it was announced that Mulhern had signed a multi-fight deal with Strikeforce. He made his debut at Strikeforce Challengers: Fodor vs. Terry and lost to Jason High via unanimous decision. Mulhern remained busy with the promotion, having won his next two bouts in Strikeforce on their Challengers series in September and November 2011. He returned in May 2012 as he faced Yuri Villefort at and won the fight via split decision. For his fifth Strikeforce fight, Mulhern was expected to face Jorge Santiago on September 29, 2012 at. However, after the event was cancelled the bout was scrapped.
Ultimate Fighting Championship
Mulhern made his UFC debut in March 2013 as he faced Rick Story on March 16, 2013 at UFC 158, replacing an injured Sean Pierson. He lost the fight via TKO in the first round. Mulhern was expected to face Ryan Couture in a lightweight bout on August 31, 2013 at UFC 164. However, Mulhern pulled out of the fight citing a hand injury and was replaced by Al Iaquinta. Mulhern was expected to face Thiago Tavares on November 9, 2013 at UFC Fight Night 32. However, Mulhern pulled out of the bout citing another injury and was replaced by Justin Salas. Mulhern faced Katsunori Kikuno on January 4, 2014 at UFC Fight Night 34. He lost the fight via unanimous decision and later announced his retirement from MMA.
Personal life
Mulhern attended St. John's College, graduating in 2008 from their campus in Santa Fe, New Mexico with a degree in liberal arts.
