[3] While a student he acted on both stage and screen,[4] playing Paul Etheridge in White Chameleon, Fleance in Macbeth, and Augustus in Tom Stoppard's Arcadia (1996) at the National Theatre in productions directed by Richard Eyre and Trevor Nunn.

[3] Ritson is best known in recent years for playing King Edward III in the TV miniseries World Without End (2012), the Duke of Kent in Upstairs Downstairs (2010–2012), Mr Elton in the 2009 BBC adaptation of Emma, Edmund Bertram in the 2007 ITV adaptation of Mansfield Park,[5] Giles Vicary in the BBC series Red Cap and for portraying sidekick Robert Presley in A Touch of Frost.

[6] He also played the part of Justin in The League of Gentlemen, Idek in God on Trial, and the comic lead in For Elsie, which he also co-produced.

Their second short film, More More More, starring The League of Gentlemen's Mark Gatiss, was a runner-up in the Turner Classic Movies Competition.

Ritson played the banjolele on Douglas Hodge's 2006 album Cowley Road Songs,[12] which was recorded in four days at the Blue Moon Studios in Banbury.