Early career McCann fought most of her early MMA career in Liverpool. In her early years as a fighter, she supported herself by working at
Subway, which earned her the nickname "Meatball Molly". After competing on the regional circuit, she amassed a record of 7–1 before signing with the UFC.
Ultimate Fighting Championship McCann made her UFC debut on 27 May 2018, against
Gillian Robertson at
UFC Fight Night: Thompson vs. Till. At the weigh-ins, she weighed in at 127 pounds, a single pound over the flyweight non-title fight limit of 126. She was fined 20% of her purse, which went to Robertson. She lost the fight via a rear-naked choke in round two. Her second fight came on 15 March 2019, facing
Priscila Cachoeira at
UFC Fight Night: Till vs. Masvidal. She won the fight via unanimous decision. McCann faced
Ariane Lipski on 22 June 2019 at
UFC Fight Night: Moicano vs. Korean Zombie. She won the fight via unanimous decision. Shortly after the fight, McCann signed a new four-fight contract with the UFC. McCann faced
Diana Belbiţă on 18 October 2019 at
UFC on ESPN 6. She won the fight via unanimous decision. McCann was scheduled to face
Ashlee Evans-Smith on 21 March 2020 at
UFC Fight Night: Woodley vs. Edwards. Due to the
COVID-19 pandemic, the event was eventually postponed. Instead, McCann faced
Taila Santos on 16 July 2020 at
UFC on ESPN: Kattar vs. Ige. She lost the fight via unanimous decision. McCann faced
Lara Procópio on 6 February 2021 at
UFC Fight Night: Overeem vs. Volkov. She lost the fight via unanimous decision. McCann faced
Ji Yeon Kim on 4 September 2021 at
UFC Fight Night 191. She won the fight via unanimous decision. The back-and-forth bout won both contestants the
Fight of the Night bonus award. McCann faced
Luana Carolina on 19 March 2022 at
UFC Fight Night 204. She won the fight via knockout in round three. With this win, she received the
Performance of the Night award. McCann faced
Hannah Goldy on 23 July 2022 at
UFC Fight Night 208. She won the fight via technical knockout in round one. This win earned her the
Performance of the Night award. As the first bout of her new eight-fight contract, McCann faced
Erin Blanchfield on 12 November 2022 at
UFC 281. She lost the fight via a kimura submission in round one. During the fight, McCann only landed 7 strikes in contrast to the 93 strikes landed by Blanchfield. McCann faced
Julija Stoliarenko on 22 July 2023 at
UFC Fight Night 224. She lost the fight by armbar submission in the first round. In her first strawweight bout, McCann faced
Diana Belbiţă in a rematch on 3 February 2024 at
UFC Fight Night 235. She won the fight via an armbar in round one. This fight earned her the
Performance of the Night award. McCann faced Bruna Brasil on 27 July 2024, at
UFC 304. She lost the fight by unanimous decision. McCann was scheduled to face Istela Nunes on 22 March 2025 at
UFC Fight Night 255. However, Nunes withdrew from the fight due to visa issues and was replaced by promotional newcomer Alexia Thainara. She lost the fight via a rear-naked choke submission in the first round and announced her retirement from mixed martial arts competition after the bout. ==Professional grappling career==