After compiling a record of 17–9, Harris signed with BAMMA in 2010, making his debut against Irish featherweight Steve McCombe at BAMMA 2, winning via unanimous decision. He followed that up with another decision victory over Neil Seery at BAMMA 3. After a 21-month layoff, Harris dropped two weight classes to take on Canadian grappler Remi Morvan at Cage Warriors 46, winning by triangle armbar at 4:21 of round 1, his first submission win since 2007. Less than a month later, he took on TUF 14 contestant Casey Dyer at Cage Warriors: Fight Night 4, notching his fifth consecutive win with a unanimous decision.
On 16 August 2012, Harris was signed by the Ultimate Fighting Championship. He made his UFC debut against fellow grappler Darren Uyenoyama at UFC on FX 5 on 5 October 2012, replacing an injured Louis Gaudinot. Harris was submitted in the second round with a rear naked choke. Harris next faced Ulysses Gomez on 16 February 2013 at. Harris won the bout via unanimous decision. Harris was expected to face John Lineker on 3 August 2013 at UFC 163, but Harris suffered a fractured orbital bone in training and he was replaced by José Maria. The bout with Lineker was rescheduled for 26 October 2013 at UFC Fight Night 30. Harris lost the fight by first-round TKO. Harris faced Louis Gaudinot at UFC Fight Night 37. He lost the fight via submission in the first round. However, on 20 June 2014, the loss was changed to a No Contest after it was revealed Gaudinot had failed his drug test. On 5 April 2014, Harris was released from the UFC after losing two fights in a row. On the same day that Harris was released from the UFC, 5 April 2014, it was announced that Harris had signed an exclusive five-fight deal with Cage Warriors. Harris was expected to face Kurban Gadzhiev on 18 April 2014 in the main event of Cage Warriors Fight Night 11. However Kurban Gadzhiev pulled out of the fight due to illness, thus scraping the fight. Harris faced Neil Seery in a rematch on 19 July 2014 at UFC Fight Night 46. He lost the fight via unanimous decision. On 31 December 2014, Harris announced his retirement from mixed martial arts.
