Born in Edinburgh, King is the daughter of Australian actor Jonathan Hyde and Scottish opera singer Isobel Buchanan.

[2] Although King grew up dreaming of being a director, she got her break into acting when she was 18 and still working at a cheese shop,[3] making her professional debut as Rosamond Oliver in Jane Eyre.

A source stated that "a week before the day she began filming, King felt stomach pains, then had her appendix rupture.

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.

[7] She appeared in the comedy horror film Cockneys vs Zombies as a bank robbery hostage trying to escape from a zombie-infested London.