Her portrayal of Pamela Anderson in the biographical series Pam & Tommy (2022) earned her nominations for a Golden Globe and a Primetime Emmy Award.

[5] Her maternal grandmother was French, and fled her village near Paris because of the Nazis, later marrying James' grandfather, a minister in the Royal Air Force.

[8] Her television credits include Ethel Brown in the 2010 BBC production of Richmal Crompton's Just William, Poppy in the fourth series of ITV's Secret Diary of a Call Girl (2011), and Lady Rose Aldridge in Downton Abbey.

[11] In 2011, James played Taylor at the Young Vic Theatre in Tanya Ronder's stage adaptation of the novel Vernon God Little directed by Rufus Norris,[12] Nina in Russell Bolam's modern adaptation of The Seagull at Southwark Playhouse, and Desdemona in Daniel Evans' production of Othello at the Crucible Theatre, Sheffield, with Dominic West and Clarke Peters.

[13] James played the role of Korrina in the Warner Brothers film Wrath of the Titans and starred in Fast Girls, written by Noel Clarke, centered around a group of young female athletes competing in the World Championships.

[14] James was photographed by Annie Leibovitz as Cinderella, in the blue gown her character wears to the ball, for the December 2014 issue of Vogue.

She also headlined the Second World War drama film The Exception, playing a British agent posing as a servant to the exiled Kaiser Wilhelm II.

In 2020, James played the second Mrs de Winter in an adaptation of Daphne du Maurier's Gothic romance Rebecca directed by Ben Wheatley and co-starring Armie Hammer.

[22] In June 2023, it was announced that James would star in Penelope Skinner’s new play Lyonesse at the Harold Pinter Theatre, alongside Kristin Scott Thomas, whom she previously acted with in Darkest Hour and Rebecca.

[29] In 2021, James began dating American musician and songwriter Michael Shuman, a member of U.S. rock band Queens of the Stone Age.