Barrit is best known for his stage work, appearing in The History Boys at Wyndham's Theatre portraying the general studies teacher, Hector, made famous by Richard Griffiths in the film version. In 2003, he played Shylock in the Chichester Festival Theatre's production of Shakespeare's The Merchant of Venice. On 7 July 2008, he took over the role of The Wizard from Nigel Planer in the West End production of Wicked at the Apollo Victoria Theatre. Originally set to begin 9 June, his performance had to be postponed to undergo an operation. Beginning 12 December 2011, he returned to Wicked, reprising his role of the Wizard, taking over from Clive Carter. He ended his third return engagement with the show on 7 July 2012 (four years after his debut), and was replaced three weeks later by Keith Bartlett. In 2014, he appeared as Michaud in Helen Edmundson's adaptation of Therese Raquin at the Theatre Royal, Bath.
- They Seek Him Here (2007) as Raymond Clandillon
- Murder on St. Malley's Day (2002) as Jonathan Eckersley-Hyde