Choi started getting noticed in the MMA world after making his DEEP debut in June 2010, when he faced Yusuke Kagiyama. Choi lost his Deep debut via split decision. After a short stint on the independent circuit, Choi returned to DEEP in September 2010, facing Atsuhiro Tsuboi. He won by TKO in the first round. He went undefeated in his next fights in MMA, beating various fighters like Mitsuhiro Ishida, Kosuke Omeda, and Nobuhiro Obiya. Before being released to fight in the UFC, Choi fought for DEEP one last time, on June 15, 2013, when he faced Japanese prospect Shoji Maruyama. He won via TKO in the second round.
While fighting for DEEP, Choi also signed with Sengoku Raiden Championship. He had his first fight at SRC: Sengoku Raiden Championship 13, when he faced Ikuo Usuda. Choi won via split decision. A few months later, Choi was slated to face Masanori Kanehara at SRC: Sengoku Raiden Championship 15. However, three weeks before the event, Choi suffered an injury and the fight was taken off the card.
Ultimate Fighting Championship
In November 2013, following a nine-fight winning streak, Choi signed a contract to fight with the UFC to compete in their featherweight division. Choi was scheduled to face Sam Sicilia on May 24, 2014, at UFC 173. However, Choi pulled out of the bout with an injury. Choi ultimately made his debut when he faced Juan Puig on November 22, 2014, at UFC Fight Night 57. He won the fight via TKO just 18 seconds into the first round. A rescheduled bout with Sam Sicilia was expected to take place on July 15, 2015, at UFC Fight Night 71. However, Choi pulled out of the fight in late June for undisclosed reasons. The bout with Sicilia was scheduled a third time and took place on November 28, 2015, at UFC Fight Night 79. Choi won the fight via knockout in the first round. The win also earned him his first Performance of the Night bonus award. Choi next faced Thiago Tavares on July 8, 2016, at. He won the fight via knockout in the first round. Choi faced Cub Swanson on December 10, 2016, at UFC 206. He lost the fight via unanimous decision. The fight was nominated for Fight of the year by the World MMA Awards and ESPN. Both participants were awarded Fight of the Night. Choi was briefly linked to a bout with Renan Barão which was expected to take place on April 15, 2017, at UFC on Fox 24. However, as the announcement of the pairing began to circulate, Choi declined the bout, and as a result, Barao is expected to be rescheduled against a different opponent, possibly at another event. Choi was expected to face Andre Fili on July 29, 2017 at UFC 214. However, Choi pulled out of the fight on June 14 citing an injury and was replaced by promotional newcomer Calvin Kattar. Choi next faced Jeremy Stephens on January 14, 2018 at. He lost the fight via TKO in the second round. Both participants were awarded Fight of the Night. Choi faced Charles Jourdain on December 21, 2019 on UFC on ESPN+ 23. Despite knocking Jourdain down in the first round, Choi eventually lost the fight via TKO in the second round. Both participants were awarded Fight of the Night.
Championships and achievements
Mixed martial arts
Ultimate Fighting Championship
*Performance of the Night vs. Sam Sicilia and Thiago Tavares
*Fight of the Night vs. Cub Swanson, Jeremy Stephens, and Charles Jourdain
