In December 2013, it was announced that Theodorou would be a cast member on, representing Canada at Middleweight. He defeated Zein Saliba in the Quarterfinals and defeated Tyler Manawaroa in the semifinals. After semifinals, he went to Phuket Province, Thailand, to train at Tiger Muay Thai with coach Patrick Côté.
Ultimate Fighting Championship
Theodorou defeated MFC vet Sheldon Westcott via TKO due to punches and elbows in the second round at to win the Middleweight tournament. Theodorou faced Bruno Santos on October 4, 2014 at UFC Fight Night 54. He won the fight via unanimous decision. Theodorou faced Roger Narvaez on March 14, 2015 at UFC 185. After a first round in which Narvaez seemed to control, Narvaez suffered a broken arm in the second round after an attempt to block a kick from Theodorou. Subsequently, Theodorou was able to get a TKO stoppage with a flurry of punches shortly thereafter. Theodorou faced Thiago Santos on December 10, 2015 at UFC Fight Night 80. He lost the fight by unanimous decision. Theodorou next faced Sam AlveyJune 18, 2016 at UFC Fight Night 89. The bout remained on the feet for nearly all of its duration in a largely uneventful fight where neither fighter was able to deliver any significant offense. He won the fight via unanimous decision. Theodorou faced Cezar Ferreira on February 19, 2017 at UFC Fight Night 105. He won the fight via a controversial unanimous decision. Theodorou faced Brad Tavares on July 7, 2017 at. He lost the fight by unanimous decision. Theodorou faced Dan Kelly on November 19, 2017 at UFC Fight Night 121. He won via unanimous decision. Theodorou faced Trevor Smith on May 27, 2018 at UFC Fight Night 130. He won the fight via unanimous decision. Theodorou was expected to face Antônio Carlos Júnior on September 22, 2018, at UFC Fight Night 137. However, Júnior pulled out on August 28 due to injury. The pairing was expected to be left intact and rescheduled for December 8, 2018, at UFC 231. On September 13, 2018, it was reported that Júnior was forced to withdraw from his bout with Theodorou yet again, citing a surgery is required on the injury that caused the cancellation of his first scheduled bout with Theodorou. On October 1, 2018, it was reported Júnior was replaced by Eryk Anders. Theodorou won the fight via a highly controversial split decision. Theodorou faced Derek Brunson on May 4, 2019, at UFC Fight Night 151. He lost the fight by unanimous decision. On May 26, 2019 it was reported that Theodorou was released by the UFC.
Post-UFC career
At the first bout after UFC release, Theodorou fought Hernani Perpetuo at Prospect Fighting Championships 12 on December 6, 2019. He won the fight in the third round via TKO.
Championships and awards
Extreme Cage Combat
*ECC Middleweight Championship
North American Allied Fight Series
*NAAFS Middleweight Championship
Ultimate Fighting Championship
*
Other ventures
Theodorou and his girlfriend, Max Altamuro, a retail manager living and working in Toronto, competed on the third season of The Amazing Race Canada. They placed 12th in their current home city of Toronto and were the first team to be eliminated from the race. Theodorou also serves as a "ring boy" for the all-female MMA promotion Invicta Fighting Championships. Theodorou is involved in an upcoming film called Last Hit in which he will portray an MMA fighter who is forced to retire but then takes up e-sports.
