Duffy started his career as a welterweight, fighting in various regional promotions across the UK and Ireland. Duffy defeated the former UFC two-weight champion, Conor McGregor, and Northern Irishman
Norman Parke, who later went on to the join the UFC. It was after this fight that Duffy signed with
Cage Warriors, the biggest MMA promotion in Europe.
The Ultimate Fighter In February 2010, Duffy was announced as a cast member of
The Ultimate Fighter 12 where he competed as a lightweight. In his first fight, Duffy lost to Kyle Watson via rear-naked choke in the first round, and was subsequently eliminated from the show.
Cage Warriors Fighting Championship Duffy made his name and rose to prominence while fighting under the
CWFC banner. In his first bout with the promotion, Duffy submitted
Conor McGregor, another Irish fighter who went on to UFC stardom. In 2011, Duffy earned a Cage Warriors title shot against Ivan Musardo. Duffy lost the fight, breaking his hand in the third round, and being subsequently submitted in the fourth. Following his recovery, Duffy switched his attention to pro boxing. He amassed a 7–0 record before returning to Cage Warriors in 2014. Duffy's first fight back was against Frenchman, Damien Lapilus. Duffy won via rear-naked choke, 2 minutes and 18 seconds into the third round. Three months later he defeated another Frenchman, Julien Boussuge. This time detecting his opponent's intention for a takedown, and connecting a clean knee to the head when Boussuge changed levels. It was an instant knockout.
Ultimate Fighting Championship In January 2015, the UFC announced they had signed Duffy. Duffy was expected to make his promotional debut against
Vagner Rocha on 14 March 2015 at
UFC 185. However, Rocha pulled out of the bout in early February citing injury and was replaced by
Jake Lindsey. Duffy won the fight via TKO in the first round after wobbling his opponent with a head kick and then dropping Lindsey with a body shot, forcing the stoppage. Duffy faced
Ivan Jorge on 18 July 2015 at
UFC Fight Night 72. He won the fight via submission in the first round. He also earned a
Performance of the Night bonus. Duffy was expected to face
Dustin Poirier on 24 October 2015 at
UFC Fight Night 76. However, Duffy pulled out of the fight on 21 October citing a concussion he incurred during a sparring session. In turn, the pairing was rescheduled, and took place on 2 January 2016 at
UFC 195. Duffy lost the fight by unanimous decision (30–26, 30–27, 30–27). Duffy next faced
Mitch Clarke on 7 July 2016 at
UFC Fight Night 90. He won the fight via submission in the opening minute of the first round. Duffy faced
Reza Madadi on 18 March 2017 at
UFC Fight Night 107. He won the fight by unanimous decision. On 13 July 2017, Duffy's manager Graham Boylan revealed Duffy had signed a new seven-fight contract with UFC. Duffy faced
James Vick on 4 November 2017 at
UFC 217. He lost the fight via TKO in the second round. Duffy was expected to face
Ross Pearson on 2 December 2018 at
UFC Fight Night 142. However, Pearson announced on 7 November that he was out of the bout due to a broken nose and subsequent surgery to correct the injury. and he was replaced by newcomer
M-1 Global Lightweight Champion
Damir Ismagulov. In turn Duffy pulled out from the event, citing a rib injury. Duffy faced
Marc Diakiese on 16 March 2019 at
UFC Fight Night 147. He lost the fight by unanimous decision. Duffy faced
Joel Álvarez on 19 July 2020 at
UFC Fight Night 172. He lost the fight via a guillotine choke in round one. After the fight, Duffy announced his retirement from MMA competition. ==Championships and accomplishments==