Cannonier began his amateur mixed martial arts career in early 2011, winning his first two fights by knockout. In June 2011, he made his professional MMA debut in Alaska. He fought sporadically over the next five years, amassing a record of 7-0.
In October 2014, it was announced that Cannonier had signed with the UFC. In his debut he faced Shawn Jordan in a Heavyweight bout at UFC 182 on January 3, 2015. He lost the fight via knockout in the first round.
2016
After an 18-month long layoff, Cannonier returned to face Cyril Asker on April 10, 2016 at. He defeated Asker by knockout due to a combination of elbows and punches. The win also earned Cannonier his first Performance of the Night bonus award. In his third fight for the promotion, Cannonier moved down a weight class to the light heavyweight division. He faced Ion Cuțelaba on December 3, 2016 at. Cannonier won the fight by unanimous decision. The bout also won Cannonier his second consecutive bonus award as he and Cuțelaba won Fight of the Night.
2017
Cannonier faced Glover Teixeira on February 11, 2017 at UFC 208. He lost the fight by unanimous decision. Cannonier was expected to face Steve Bossé on July 7, 2017 at. However, Bossé was removed from the fight just days before the event and was replaced by promotional newcomer Nick Roehrick. Cannonier won the fight via TKO in the third round. Cannonier was expected to face Antônio Rogério Nogueira on December 16, 2017 at UFC on Fox 26. However, on October 19, it was announced that Nogueira was pulled from the card after being notified by USADA of a potential doping violation. Cannonier would face Jan Błachowicz instead. He lost the fight via unanimous decision.
Cannonier faced former UFC Middleweight champion Anderson Silva on May 11, 2019 at UFC 237. He won the fight via TKO in the first round after a kick to Silva's right leg rendered him unable to continue. Cannonier faced Jack Hermansson on September 28, 2019 in the main event of UFC on ESPN+ 18. He was victorious via second-round TKO. The win also earned Cannonier his third Performance of the Night bonus award.
2020
Cannonier was scheduled to face former UFC Middleweight ChampionRobert Whittaker on March 7, 2020 at UFC 248. Cannonier was slated to serve as a backup fighter for the UFC Middleweight Championship fight between Israel Adesanya and Yoel Romero at UFC 248 on March 7, 2020, however, on February 14, 2020, Cannonier announced he had suffered a torn pectoral muscle and expects to be out of action for six months. Cannonier is scheduled to face Robert Whittaker on October 24, 2020 at UFC 254.
