Between 2013 and 2015, Mimi was a series regular in EastEnders, playing Cindy Williams. For her role, she earned British Soap Award and Inside Soap Award nominations. She voiced Euryale, Stheno, and Medusa in the 2013 video game Castlevania: Lords of Shadow – Mirror of Fate and its 2014 sequel Castlevania: Lords of Shadow 2. In 2016, she appeared in an episode of Casualty as Lana Westmore,[8] and played Megan in a short film, The Escape, in 2017. In 2019, she portrayed the younger version of Edith Tolkien in Tolkien, also in 2019 she began playing Ruby Matthews in the Netflix series Sex Education and appeared in the film Close. In 2023, Keene appeared in the film After Everything.