Early career He made his professional debut competing as a featherweight for various regional promotions across Great Britain, including a stint in
Cage Warriors. He was able to compile a record of 9–1 in his first three years along the way. After his TKO stoppage of Paul Cook in November 2014, Allen signed with the UFC.
Ultimate Fighting Championship Allen made his promotional debut on 20 June 2015 as a short notice replacement filling in for an injured
Mike Wilkinson against Alan Omer at
UFC Fight Night 69. After probably dropping the first two rounds, Allen won the fight via submission in the third round. He was also awarded a
Performance of the Night bonus. Allen next faced
Yaotzin Meza on 27 February 2016 at
UFC Fight Night 84. He won the fight by unanimous decision. Allen was expected to face
Mirsad Bektic on 8 October 2016 at
UFC 204. However, due to injury, Allen withdrew from the fight and was replaced by
Russell Doane. Allen faced
Makwan Amirkhani on 18 March 2017 at
UFC Fight Night 107. He won the fight by split decision. Allen was scheduled to face
Enrique Barzola at
UFC 220 on 20 January 2018. However, Allen was pulled from the fight on 11 January due to alleged
visa issues which restricted his ability to travel. Following this announcement, It was determined that Allen would be replaced by
Matt Bessette at UFC 220. Allen faced
Mads Burnell on 27 May 2018 at
UFC Fight Night 130. He won the fight via front choke submission in the third round. This win earned him the
Performance of the Night award. Allen was expected to face
Gilbert Melendez on 30 November 2018 at
The Ultimate Fighter 28 Finale. However, Melendez pulled out of the fight on 5 November and was replaced by
Ricky Glenn. In turn, Allen pulled out of the fight on 16 November citing a cut he received while training. Allen faced
Jordan Rinaldi on 16 March 2019 at
UFC Fight Night 147. He won the fight by unanimous decision. Allen faced
Gilbert Melendez on 6 July 2019 at
UFC 239. He won the fight via unanimous decision. Allen was expected to face
Josh Emmett on 25 January 2020 at
UFC Fight Night 166. However Emmett was pulled from the event for an undisclosed reason, and he was replaced by
Nik Lentz whose original featherweight opponent also dropped out of the event. Allen won the fight via unanimous decision. Lentz would later claim he lost 40% of his vision after being poked in the eye by Allen. Allen was scheduled to face
Jeremy Stephens on 7 November 2020 at
UFC on ESPN: Santos vs. Teixeira. However, Stephens was forced to withdraw from the event, citing injury. In turn, the bout was cancelled. Allen faced
Sodiq Yusuff on 10 April 2021 at
UFC on ABC 2. After knocking Yusuff down twice, he won the fight via unanimous decision. Allen faced
Dan Hooker at
UFC Fight Night 204. He won the fight via technical knockout in the first round. With this win, he received the
Performance of the Night award. Allen faced
Calvin Kattar on 29 October 2022 at
UFC Fight Night 213, winning via technical knockout following a knee injury to Kattar. Allen faced former
UFC Featherweight champion
Max Holloway on 15 April 2023 at
UFC on ESPN 44, where he lost via unanimous decision, ending his win streak in the UFC. Allen faced
Movsar Evloev on 20 January 2024, at
UFC 297. In a competitive bout, he lost by unanimous decision. Allen faced
Giga Chikadze on 27 July 2024, at
UFC 304. He won the fight by unanimous decision. Allen faced
Jean Silva on 24 January 2026, at
UFC 324. He lost the fight via unanimous decision. Allen is scheduled to face Melquizael Costa on 16 May 2026 in the main event at
UFC Fight Night 276. ==Personal life==