She is best known for her role as Jo Portman in the BBC One television drama series Spooks in which she appeared between 2005 and 2010.
In April 2007, she appeared in Doctor Who, Daleks in Manhattan and Evolution of the Daleks. Her character Tallulah was a show girl, whose opening scene was on stage dancing and singing to a musical number—her father, Nick Raison, played the piano background as part of the BBC Welsh Symphony Orchestra. She was a guest on the second series of Totally Doctor Who in episode 4.
In 2007 she appeared in the Channel 4 series Comedy Showcase of six episodes of Plus One, alongside Duncan James, Rory Kinnear and Nigel Harman.
In 2010 she starred in the ITV1 comedy-drama Married Single Other as a model called Abbey.
Raison played the title role in Anne Boleyn, a new play by Howard Brenton which premiered at Shakespeare's Globe on July 24, 2010, to much critical acclaim. In the same Shakespeare's Globe season she played Anne Boleyn in Henry VIII by William Shakespeare.
In 2011 she returned to the BBC1 in Sugartown, a three part comedy/drama, aired on BBC1, and again in crime comedy-drama Death in Paradise. Also in 2011 she played the role of Isolde in fourth series of the BBC drama Merlin, which began airing in October. She appeared in episodes 12 and 13 "The Sword in the Stone" Part I and Part II.