His first screen appearance was as a youth being interviewed by the police in an episode of
The Bill in 1995; he was then cast in other UK TV dramas before he made his feature film debut as Johnny Silver in
Jez Butterworth's
directorial debut,
Mojo. He had created the same role in the stage premiere at the
Royal Court Theatre in July 1995. He followed the film
Mojo with
Stella Does Tricks, playing a young male prostitute hooked on drugs who befriends Stella, a 15 year old prostitute. Matheson then played Marius in
Bille August's film version of
Les Misérables, appearing alongside
Liam Neeson,
Geoffrey Rush and
Claire Danes, where he "was determined to play him as a heartfelt revolutionary, demanding power for the people". When he went to New York it was the first time he had left the UK in what he described shortly after as "an unbelievable turn of events". In 2000 he starred in
Canone Inverso set in the 1930s, as Jeno Varga, a young man who falls in love with a pianist; he learnt the violin for this role. The actor visited Pasternak's niece in Oxford, and on reading some of the Russian poetry (in translation by his sister) was "inspired beyond belief"; and saw it as a "great opportunity to play a wonderful character with such a huge range of emotions". Despite inevitable comparisons with the 1965 Lean film, his portrayal - "intense, playful, assured and able to convey a very effective sense of trouble brewing" was praised, and another critic commended the "outstanding performances", noting how "Matheson's sunken eyes capture the toll Zhivago's travails exact upon him, both spiritually and physically". Matheson played a private in the trenches in the 2002 horror war film
Deathwatch, then in early 2004 he starred as an alcoholic in rehab in the television docu-film
Comfortably Numb, which he later described as "his proudest role". one described Matheson's performance as "as affecting as it was understated", adding "I haven't seen anyone command the small screen so effectively in a long time. In 2006, Matheson co-starred as a lighthouse-keeper who has a romance with murder mystery author
Demi Moore in the film
Half Light. He then portrayed the
Earl of Essex in a BBC production about Queen
Elizabeth I of England called
The Virgin Queen, broadcast in the US in 2005 and the UK in 2006. For this role, he sought to emulate the swagger of
Marc Bolan, listening a lot to Bolan and
Kurt Cobain (for his aggression) in the dressing room; he added "I really, really loved playing this character ...with Essex I felt I had to constantly come outside of my safety zone, which was very liberating for me". Another period drama followed when he appeared as Archbishop
Thomas Cranmer in the second season of the
Showtime series
The Tudors in 2008. The same year Matheson played Alec Stoke-d'Urberville, "calculating and spoilt, but also friendly and charming" in the four-part
BBC adaptation of ''
Tess of the d'Urbervilles''. His was not the one-note villain, rather a damaged and misguided individual; "I tried to find something in his story. I don't think that he ever intended to hurt Tess and I think he believed he loved her, but in reality it was more of an obsession", Matheson commented later. while another critic added that the "relationship between Tess and Alec is extremely well portrayed". Matheson then played Argive archer Ixas in the 2010
Clash of the Titans remake. he starred in
The Christmas Candle as Reverend David Richmond. He considered the film more as a "romantic comedy", and not a message of Christian faith, and was drawn to the idea of an authority figure, vicar, who humbly realises that there is much more for him to learn. He had a supporting role as
Aeschylus in
300: Rise of an Empire, which required him to get fit in about ten weeks through hard-core training. In 2015 he was cast in the lead role of John Blackwood (Johnny Jackson) a "flawed" but "lovable rogue", who is seeking redemption from actions committed in his past in the
ITV series
Jericho, which aired in January 2016 in the UK; but the drama was not continued after its first series. ==Approach to acting==