Atkins' breakthrough came early, in Shane Meadows' 2002 film Once Upon a Time in the Midlands, in which she played Marlene, the daughter of Shirley (Shirley Henderson) and Jimmy (Robert Carlyle). Although opinions on the film were divided, everyone seemed to agree about Atkins' contribution. Evening Standard Journalist Neil Norman, in his review of the film in the Daily Mail, stated that it contained "good performances from everyone — and a stunning one from 12-year-old Finn Atkins… she can hold the screen like a pro and takes a close-up better than many actors twice her age." In The Guardian, Peter Bradshaw wrote of the film: "there is a cracking turn from Finn Atkins as Shirley's daughter… a bouquet is due." Whilst The Telegraph's Sukhdev Sandhu exclaimed: "Finn Atkins is superb as Shirley Henderson's whey-faced daughter."

In January 2009 she appeared as teenage prostitute Marissa in the BBC One soap opera EastEnders. She has since become a regular in Sky1's hit comedy drama 'Starlings' where she plays Charlie Starling; the football mad daughter to Jan & Terry Starling (Lesley Sharp & Brendan Coyle).