Lawson has been a freelance contributor to numerous publications since 1984, beginning on The Universe in that year, and for The Times from 1984 to 1986. He has written a column for The Guardian since 1995, having previously written for The Independent (1986–95), and has twice been TV Critic of the Year as well as winning many other journalism awards. However, his Guardian journalism has not been universally admired and Richard Gott, a former colleague, has commented that the "prevalence of the bland and the obsequious" on The Guardian is typified by Lawson's "embedded presence".

Lawson presented The Late Show on BBC2 in the 1990s and presented its offshoot The Late Review (later Sunday Review and from 2000 Newsnight Review) until the 2005 "review of the year" edition of Newsnight Review, broadcast on 16 December, which marked the end of his association with the format. In 2004, Lawson made a documentary for BBC Four called The Truth About Sixties TV, criticising what he called "golden ageists" who, he said, have a rose-tinted view of television's past.

In addition to his work in print journalism and the broadcast media, Lawson has written five books, both fiction and non-fiction. His first, Bloody Margaret (1991), is a collection of novellas on late 20th-century politics in the UK, including an eponymous satire concerning Margaret Thatcher. This was followed by The Battle for Room Service (1993), a travelogue of people, politics and culture encountered by Lawson as a Journalist. His 1995 book, Idlewild, is an alternative history novel in which both John F. Kennedy and Marilyn Monroe survived the 1960s. Going Out Live (2001) focused on contemporary Celebrity culture and the media, and Enough is Enough (2005) is a satire set in the government of Harold Wilson during the late 1960s.

Lawson became the main presenter of BBC Radio 4's daily arts programme, Front Row, in 1998. He has written several radio plays for the network, including St Graham and St Evelyn (2003) on the friendship between the Catholic novelists Graham Greene and Evelyn Waugh and The Third Soldier Holds His Thighs (2005) on Mary Whitehouse's unsuccessful litigation against the National Theatre production of Howard Brenton's play The Romans in Britain. He has also written episodes of the television version of the BBC sitcom Absolute Power appearing as himself in the series 1 episode 2, "Pope Idol", and is one of many celebrities impersonated by the Dead Ringers team, referred to as "Britain's brainiest potato" and "the thinking woman's potato" because of his baldness. In 2002, Viz ran a spoof of his Newsnight Review programme, featuring Lawson engaged in a desperate search for hard-core pornography, entitled "The Artful Podger".

Lawson chaired the judges for the 2011 Hippocrates Prize for Poetry and Medicine. His in-depth, one-to-one interviews for BBC Four, entitled Mark Lawson Talks to …, have been running since 2006.

Lawson's connection with Front Row ended in March 2014 for "personal reasons" in a joint agreement with the BBC. An internal report completed in January investigated claims of bullying within the BBC Radio Arts, which produces Front Row, and identified one Producer and presenter as responsible. While Lawson has denied bullying, The Daily Telegraph reported on 5 March that Lawson was the presenter involved and he had been accused of "browbeating junior staff" who are often young freelancers. In Lawson's 2016 novel The Allegations, a lecturer at a fictional English university faces disciplinary action and dismissal for "B&H" (bullying and harassment). The charge sheet faced by Dr Tom Pimm includes such heinous crimes as sighing during departmental meetings, "divisive social invitations" and "visual Insubordination (sic) towards senior management". Pimm's Kafkaesque hearing during which he is told by his chief persecutor that "if someone felt you were being insensitive then, to all intents and purposes, you were", might be read as Lawson's satirical comment on his own treatment at the hands of the BBC, though the author is careful to distance himself from any such interpretation in his Afterword.