Gagnon began training in 2006 and made his professional MMA debut in September 2008. He fought exclusively in his native Canada and amassed a record of 8-1 before joining the Ultimate Fighting Championship.
Gagnon was expected to make his UFC debut in Chicago, Illinois at UFC on Fox 2 against The Ultimate Fighter 14 alumnus Johnny Bedford. On January 25, 2012, the UFC announced the bout was cancelled due to Gagnon's visa issues.
Gagnon faced Bryan Caraway on July 21, 2012 at UFC 149. He lost the fight via submission in the third round. Despite the loss, Gagnon was given a Fight of the Night bonus award for his performance.
Gagnon next faced Walel Watson on September 22, 2012 at UFC 152. He won the fight via submission in the first round.
Gagnon was expected to face Issei Tamura on March 16, 2013 at UFC 158. However, Gagnon was forced out of the bout with an injury and was replaced by T.J. Dillashaw.
Gagnon next faced Dustin Kimura on September 21, 2013 at UFC 165. He won the fight via submission in the first round. The win also earned him his first Submission of the Night fight bonus.
Gagnon was expected to face Alex Caceres on December 7, 2013 at UFC Fight Night 33. However, the bout was scrapped during the week leading up to the event due to an alleged visa issue for Gagnon, restricting his entry to Australia.
Gagnon faced promotional newcomer Tim Gorman on April 16, 2014 at The Ultimate Fighter: Nations Finale. He won the bout via unanimous decision.
Gagnon was expected to face Aljamain Sterling on October 4, 2014 at UFC Fight Night: MacDonald vs. Saffiedine. However, Sterling pulled out of the bout and was replaced by Rob Font. Subsequently, Font pulled out of the fight the week of the event and was replaced by Roman Salazar. Gagnon won via submission in the first round.
Gagnon faced Renan Barão on December 20, 2014 at UFC Fight Night 58. He lost the fight via an arm-triangle submission in the third round.
Gagnon returned from a near two year hiatus to face Matthew Lopez on December 10, 2016 at UFC 206. He lost the fight via unanimous decision.
Gagnon was expected to face Brett Johns on July 16, 2017 at UFC Fight Night 113. However, Gagnon was removed from the card on 27 June and replaced by Albert Morales.Ultimate Fighting Championship
Fight of the Night (One time)
Submission of the Night (One time)