Whilst attending Highgate Wood School Arts College, Johnson was spotted by an agent in a production of Guys and Dolls, in which she played the lead.

[4] In the same year she also appeared as the lead in the acclaimed UK tour of Henry James' Daisy Miller directed by Christopher Morahan[5] and in the pantomime Cinderella at Stafford's Gatehouse Theatre.

[6] In 2009 she played Mindy in a revival of Aunt Dan and Lemon at the Royal Court Theatre,[7] receiving positive notices in the Evening Standard, The Guardian and The Times.

[8] In April 2010, Johnson was cast by Warner Bros. in The CW network's US TV pilot Damn Thorpes (aka The Wyoming Project) opposite co-star Sean Faris (Vampire Diaries).

[10] She played the role of Laura Derbyshire,[11] a pregnant teenager and subsequently a new mother, in the BBC Three comedy Pramface, alongside her Beaver Falls co-star Emer Kenny.