Wilson was born in Ashford, Kent and raised with three older brothers in Shepperton, Surrey. She attended Notre Dame School and sixth form at Esher College. As a teenager, Wilson worked in modeling, and went on to study history at the University of Nottingham. She later trained at and graduated from the London Academy of Music and Dramatic Art in July of 2005. Afterwards, she co-founded Hush Productions.

Prior to her role in Jane Eyre, Wilson had only one professional screen credit, in Suburban Shootout, a situation comedy. Since then, Wilson has stated she is "going to better auditions. People are starting to see me, when they wouldn't have done, before - suddenly you have done a big show, and have got a bit more standing."

Wilson's performance in Jane Eyre earned her four nominations for Best Actress awards in 2007, from the Broadcasting Press Guild, BAFTA television awards, Satellite Awards and the 2008 Golden Globes. She also came second in a BBC viewers poll for Best Actress of 2006.

In 2006-2007 she filmed the second series of Suburban Shootout, a new Marple mystery for ITV, and Stephen Poliakoff's BBC television drama Capturing Mary as the young Mary. Following Capturing Mary Stephen Poliakoff loved Ruth so much that he produced a forty five minute monologue for her character of Mary in Capturing Mary called 'A Real Summer'. She appeared in Gorky's Philistines, playing Tanya, at the National from May until August 2007-- and learned to play the piano for the role. In June 2007, Wilson presented the 2007 Lilian Baylis Awards.