Mark made his debut in 1987, with a brief TV appearance in an episode of the six-part 'BBC' comedy series 'The Ritz.' The following year, he appeared as ‘Mal Prentis,’ a relatively prominent character in the 'BBC' comedy–drama 'A Very Peculiar Practice.' For the subsequent 2 years, Mark did not work in any project. He made his film debut in 1990, playing the brief role of ‘Sam’ in 'Dark Romances Vol. 2.' However, his first feature-length movie came a few years later.
Continuing with TV productions, he appeared in two episodes of the 'ITV' police-procedural series 'The Bill.' He was next seen in the 'Fox' sitcom 'Married... with Children' and the police drama 'Between the Lines.' He then appeared in a brief recurring role in the British crime–drama 'Band of Gold.'
Mark turned to theater in 1990 and acted in a few prominent productions. Some of them were 'The Fantasticks' and William Shakespeare's 'Much Ado About Nothing' and 'Caesar.’ All these musicals were staged at the 'Open Air Theatre' in Regents Park in London.
From 1991 to 1992, Mark acted in a significant number of theater productions staged at London’s 'Laurence Olivier Theatre,' 'Cottesloe Theatre,' and 'Lyttelton Theatre.' Some of the plays he appeared in during the period were 'The Trackers of Oxyrhynchus,' 'The Wind in the Willows,' 'Racing Demon,' 'Murmuring Judges,' and 'The Shape of the Table.'
In the subsequent years, Mark appeared in many TV series, such as 'Peak Practice,' 'Heartbeat,' 'Out of the Blue,' and 'Sunnyside Farm.' He appeared as an angel in the short film 'Bruised Fruit' and was then seen in two TV movies, namely, 'Respect' and 'The Heart Surgeon.' Mark also appeared in seven episodes of the Rowan Atkinson-starrer sitcom 'The Thin Blue Line,' all aired in 1996.
Mark made his prominent film debut with the 1997 British comedy 'The Full Monty.' He was cast as a steelworker named ‘David "Dave" Horsefall,’ one of the leading characters of the movie. Mark received accolades for his performance in the film and bagged a 'Screen Actors Guild Award,' along with the cast, for ‘Outstanding Performance by a Cast in a Motion Picture.’ The movie also earned him two ‘Best Supporting Actor’ nominations, one each for the 'BAFTA Award' and the 'Satellite Award.'
Following brief roles in the 1998 Christmas fantasy comedy–drama film, 'Jack Frost' and the 1999 British TV comedy 'The Flint Street Nativity,' Mark delivered career-defining performances in the film 'The Flintstones in Viva Rock Vegas' and the series 'Still Standing.'
Mark was cast as ‘Fred Flintstone,’ the main character in the 2000 animated comedy 'The Flintstones in Viva Rock Vegas.' Also known as 'The Flintstones 2,' the movie was based on the animated TV series of the same name and was the prequel to the movie 'The Flintstones' that released in 1994.
Mark starred as ‘Roland,’ a squire and a loyal friend of the character ‘William,’ played by Heath Ledger, in the 2001 medieval adventure–comedy film 'A Knight's Tale.' The following year, he began his stint as ‘William "Bill" Miller’ in the 'CBS' sitcom 'Still Standing.' Mark’s character was the patriarch of the Chicago-based family in the series.
Mark’s next significant film was the 2003 mystery horror 'The Order' (also known as 'The Sin Eater'), in which he played a “Carolingian” named ‘Thomas Garrett.’ He played ‘Friar Tuck,’ the companion of the legendary hero ‘Robin Hood,’ in the 2010 British–American epic historical drama 'Robin Hood.' The same year, he played ‘Detective O'Hearne’ in the Canadian comedy–drama film 'Barney's Version.'
Some of his notable theater roles were those of ‘Kevin Snell’ in the 2006 revival of Michael Frayn’s 'Donkeys' Years,' ‘Dogberry’ in 'Much Ado About Nothing,' and the real-life Norwegian polar explorer Hjalmar Johansen in 'Fram.' In 2009, Mark was signed by 'Tesco Clubcard,' the loyalty card of British supermarket chain 'Tesco,' for its series of advertisements. He played ‘John Piggott’ in the 2009 film 'Red Riding: In the Year of Our Lord 1983,' based on the Yorkshire Ripper killings from 1974 to 1983.
In 2011, Mark essayed the role of the fictional character ‘Robert Baratheon’ in the fantasy–drama series 'Game of Thrones.' The series is an adaptation of George RR Martin’s series of epic fantasy novels titled 'A Song of Ice and Fire.' Though Mark played the character for just seven episodes, he still succeeded to stand out in this multi-starrer series. His character was one of those few who got to sit on the famed iron throne. Mark, along with the 'Game of Thrones’ cast, was nominated for two awards: the 'Scream Award' for the ‘Best Ensemble’ and the 'Screen Actors Guild Award' for ‘Outstanding Performance by an Ensemble in a Drama Series.’ Mark was cast as NKVD officer ‘Vladimir’ in the 2011 play 'Collaborators,' staged at the 'National Theatre.'
Mark’s next recurring role was as Roman hero and god ‘Hercules’ in the British fantasy-adventure 'Atlantis,' from 2013 to 2015. In 2016, he made his next significant theater appearance, as ‘Bobby Spokes’ in Richard Bean's 'The Nap' at Sheffield’s ‘The Crucible Theatre.'
Mark lent his voice to the character ‘Clyde the Horse’ in the 2018 musical fantasy film 'Mary Poppins Returns.' He also voiced the character ‘Daelin Proudmoore’ in the multi-player video game 'World of Warcraft: Battle for Azeroth.' After 'Tesco Clubcard,' Mark starred opposite Tara Fitzgerald in the British film 'The Runaways,' which is scheduled to be screened at the 'Cannes Film Festival' in May 2019.