Mark is the author of the book Business Secrets of the Pharaohs, published by the vanity publisher British London, who misspelled Mark's name as "Mark Crorigan" on the front cover. Mark threatens to sue British London for damages but also reveals that he wants his next book to be about "Napoleon and the internet" ( Business Secrets of the Pharaohs).

Unsurprisingly, Mark is highly sexually frustrated, and also apparently somewhat repressed; he is disgusted by Jeremy's licentious views (if not always practice) on easy women and kinky sexual behaviour. At first, his sexual anxiety was partly a result of a testicular hydrocele, about which he also became paranoid, but the swelling was reduced by surgery. Nevertheless, his fear that women will be unimpressed with his genitals remains firmly in place. If the class reunion invite in "Handyman" is to be believed, Mark was born in 1973. He attended Exbourne School in Shropshire until his father's British Aerospace shares crashed and he was forced to attend the state-run Fitzalan Comprehensive School. This sudden change from public to state school is believed to have left him somewhat socially damaged. He later attended University of Dartmouth, where, despite wanting to study ancient history, he was forced by his family to take business studies. His middle name is Hugh, which can be just made out in the last series four episode " Wedding", spoken near-inaudibly by the priest beneath a voiceover. He is an avid amateur historian, having always regretted not taking ancient history as opposed to business studies at university. He enjoys playing chess. He also has an interest in pop-philosophy, stating that he gets his "brain training from Sudoku and Alain de Botton's weekly podcast." Mark is very much a social reject; he is paranoid about nearly everything, thinks too much (usually for the worst) and worries endlessly about wanting to seem normal, something he never quite manages to do (indeed, his constant worrying about this suggests he has accepted that is not normal). In practice, he spends most of his time in series 1 & 2 obsessing about Sophie, then in series 3 and 4, worrying about his ever-worsening relationship with her and much of series 5 is spent worrying about the stigma of being a 'jilter'. He has been described by T.V critics as a "fifty-year-old in a thirty-something body".After his time at JLB comes to a close, Mark works as a waiter at the Mexican restaurant Banditos, a bathroom equipment salesman at Bath, Bathrooms, and Fittings, and finally again as a loan manager at Met City Bank (albeit he is fired in the series finale). In series 9, he attempts to start an affair with April, whom he knew briefly years earlier, and comes close to doing so. He ultimately fails in the series finale when he allows Jeremy and Super Hans to hold her husband captive in their flat, which she discovers. In Series 1 Episode 4, Mark ponders whether he has developed a homosexual crush on Alan Johnson, then only a visiting speaker at JLB. In an effort to explore this previously undiscovered side of his personality, Mark rents gay pornography and eventually came to the conclusion that he was "possibly bi, but basically un-curious." Alan has since become Mark's boss and Mark is still paranoid about his potential to have feelings for Alan.

His boss at JLB credit is Alan Johnson, a charismatic albeit domineering friend who seems to view Mark as something of a protege. Sophie Chapman, whom Mark met at JLB credit, goes from being the object of his neurotic affections to brief, reluctant wife, and after a long falling out they become friends looking after their son, Ian. Mark befriends Dobby and Gerard, forming a love triangle. He and Dobby have a relationship, but split when she gets work in New York. Gerard dies. That is so Gerard. A running gag is Mark's tendency to think a woman is "the one" and find out he has no feelings for them, shown mainly in Series 5 in most, if not all, of the episodes when he describes his respective love interest (most of whom only last one episode) as "the one". Mark also has a habit of thinking minor details and items will ruin or improve his life. Another running gag is Mark's tendency to use women as a way of getting revenge on others or assuring himself that he is capable of maintaining relationships. It is unclear between him and Jeremy who is the older of the two, given absolutely no information is provided about their ages or birthdates. Mark's infatuation and relationship with Sophie is a major theme of the first four series. Following their disastrous wedding and divorce, he pursues a series of other women during series 5, wondering whether each could be "the one". After a one-night stand with Sophie following their break-up, she becomes pregnant and later gives birth to Mark's child, Ian James. Mark and Jeremy share an interest in mostly the same mainstream TV series and films. Mark likes the TV show The Apprentice and Grand Designs, while often only feigning an interest in more highbrow subjects like the Victorian Arts and Crafts movement. Mark's politics are ambiguous. He is a socially conservative critic of political correctness and is uncomfortable with drug culture and openness about sexuality. He believes in the "miracle of consumer capitalism." ( Jurying) In the second series, he implies he likes Tony Blair, but in the fourth series he seems skeptical of the 2003 invasion of Iraq and by the fifth series, he says "nobody wanted New Labour" and shows admiration for Liberal Democrat Paddy Ashdown.Mark has a sister, Sarah, a solicitor who shares a great deal of Mark's social shortcomings. He often thinks fearfully of his parents, especially his father who is controlling and bullying. Mark's biggest interest is history, in particular ancient history and the Second World War. He is interested in Nazism, playing a Nazi soldier in a re-enactment watching films like Das Boot and playing WWII computer games. It is implied that his grandfather died in the Second World War. He also read the book Stalingrad.