He auditioned for the National Youth Theatre when he was 15, originally joining as a musician and writing the score for the year's production, but later switching to acting. After leaving school he studied acting at the Royal Academy of Dramatic Art (RADA) in London for three years where he won the Fabia Drake prize for comedy.
His first television work was for Granada TV, first acting as a policeman in Strangers and then getting a part in Celebration. This was followed by an appearance in Juliet Bravo, as a teenage tearaway. His first television role as one of the regular cast was in the BBC hospital drama Angels where he played Terry, an ambulance driver.
After reading the part to John Nathan Turner and Eric Saward he was soon told he was successful and chose Doctor Who in preference to staying on Angels. Mark made his debut on Doctor Who in Mawdryn Undead, televised in 1983, as Turlough, a companion to Peter Davison's fifth Doctor. His final story was Planet of Fire, in 1984. He decided to leave the programme without staying for the full eighteen months of his contract, partly as a new team were coming in (Colin Baker and Nicola Bryant were brought in to replace Peter Davison and Janet Fielding) and feeling that "with Turlough having done all he could usefully do, it was time he should go".
In 1988 he made a life-changing decision to move to Australia, despite never having previously visited the country. He carried on working as an actor but wanted to do something different, opting to study Zoology at the University of New England in Armidale and "save the world". He was taken on as a research student by Professor Fritz Geiser and gained a first class honours degree in 1994, writing his thesis on the overwintering biochemistry of the light brown apple moth. He combined studying for his degree with teaching drama there, and he was involved with setting up and developing an external (distance learning) Theatre Studies course. He also found time to appear in Police Rescue, Minder and Dolphin Bay, radio broadcasts and commercial appearances.
He capitalised on this success, moving to Head of Programming at Oxford Scientific Films in 2001, turning around the struggling company and tripling its production ouput. Under his tenure the company received an Emmy and two Golden Panda awards for Bug World. He moved to New Zealand in 2006, joining NHNZ (Natural History New Zealand), a subsidiary of National Geographic, which produced many hours of documentaries each year. Besides programmes on natural history he has also produced the popular "I Survived" series for the Biography channel and documentaries on industrial engineering. He has produced programmes for the BBC, ITV, Channel Four and the Discovery Channel and usually does the directing and writing as well. His work has been outstanding and sometimes groundbreaking; his were the first programmes to capture important information on Komodo dragons, at great personal risk. More recently (2010 - 2011) he formed his own production company and worked on a contract for the Qatari government's bid for Qatar to become a UNESCO World Heritage Site, making documentaries about the country's flora and fauna. In 2012-2013 his main focus was on filming an observational documentary series for Al-Jazeera on "Wildlife Warfare" following a group of trainee anti-poaching rangers. In 2015 he relocated to work for ITV Scotland, producing the popular series "Border Life" together with current affairs programmes and parliamentary coverage. In 2016 he returned to New Zealand, planning to produce a series on dinosaurs and write a book for children.
Occasionally he attends Doctor Who conventions and he has revisited his role as Turlough for Big Finish Audio dramas. He lives in New Zealand with his wife Lisa and son Tom.