Although King grew up dreaming of being a director, she got her break into acting when she was eighteen and still working at a cheese shop, making her professional debut as Rosamond Oliver in Jane Eyre. She was nearly unable to play the role, however, "A week before the day she began filming, King felt stomach pains, then had her appendix rupture. Her agent told the producers that she was unlikely to recover from the operation to remove it for at least ten days." Another actress was cast, but King recovered in time and was able to get the required medical clearance to film.
She is best known as Goldie, a surrogate mother in the American sitcom, The New Normal. Formerly, she was well known for her acclaimed performance as the tyrannical head-girl Harriet Bentley in 2008's Wild Child, and as cruel, conniving Sophie in the 2009 slasher film, Tormented. Also in 2009 King received critical acclaim for her performance as the manipulative Victoria in the film Tanner Hall. She also performed in One Night in November at the Belgrade Theatre in Coventry, from October to November 2010, as well as being featured in the 2011 film Chalet Girl. She appeared as Princess Elena in the episode "The Changeling" of the third series of the BBC's Merlin. She starred in the comedy horror film Cockneys vs Zombies as a bank robbery hostage trying to escape from a zombie-infested London. The film also stars Michelle Ryan, Rasmus Hardiker, and Jack Doolan, and was released in 2012.