Early career Starting his professional career in 2013, Mullarkey compiled a 12–2 record on the regional Australian scene, winning the UFN Lightweight Championship, Super Fight MMA Lightweight Championship, and BRACE Featherweight Championship in the process.
Ultimate Fighting Championship Mullarkey made his UFC debut against fellow newcomer,
Brad Riddell at
UFC 243 on 5 October 2019. He lost the bout via unanimous decision but took home the
Fight of the Night bonus. Mullarkey was expected to face
Jalin Turner on 3 February 2020 at
UFC Fight Night 168. However Mullarkey was forced to withdraw from the bout due to injury and he was replaced by
Joshua Culibao. Mullarkey made his sophomore appearance in the organization against
Farès Ziam at
UFC Fight Night: Ortega vs. The Korean Zombie on 18 October 2020. He lost the fight via unanimous decision. Mullarkey faced
Khama Worthy at
UFC 260 on 27 March 2021. He won via knockout within the first minute of the bout. Mullarkey faced
Devonte Smith on 2 October 2021 at
UFC Fight Night 193. He won the fight via technical knockout in round two. This win earned him the
Performance of the Night award. Mullarkey faced
Jalin Turner on 5 March 2022 at
UFC 272. He lost the fight via technical knockout in round two. Mullarkey faced
Michael Johnson on 9 July 2022 at
UFC on ESPN: dos Anjos vs. Fiziev. He won the fight via split decision. The bout earned the
Fight of the Night bonus award. Mullarkey was scheduled to face
Magomed Mustafaev on 22 October 2022 at
UFC 280. However, Mullarkey pulled out in mid-September due to injury. Mullarkey was scheduled to face
Nasrat Haqparast on 12 February 2023, at
UFC 284. However, Haqparast withdrew due to undisclosed reason and was replaced by promotional newcomer Francisco Prado. He won the fight via unanimous decision. Mullarkey was scheduled to face Guram Kutatuledze on 3 June 2023, at
UFC on ESPN 46. However, Kutatuledze withdrew from the bout and was replaced by
Muhammad Naimov. Mullarkey lost the bout via technical knockout in the second round. Mullarkey faced
John Makdessi on 10 September 2023, at
UFC 293. He won the fight by unanimous decision. Mullarkey faced
Nasrat Haqparast on 9 December 2023 at
UFC Fight Night 233. He lost the fight via knockout in round one. Mullarkey faced
Maurício Ruffy on 4 May 2024, at
UFC 301. He lost via TKO stoppage at the end of the first round. Mullarkey faced Rolando Bedoya on 28 September 2025 at
UFC Fight Night 260. He won the fight via unanimous decision. Replacing
Rong Zhu, Mullarkey faced
Quillan Salkilld on February 1, 2026, at
UFC 325. He lost the fight via a rear-naked choke submission in the first round. ==Championships and accomplishments==