One of his earliest breaks was as the sole British writer for The Muppet Show. He also appeared as the “special guest star” in the nineteenth episode of the final season, when the scheduled guest, Richard Pryor, was unable to make it to the recording; a script was hastily written in which “Chris the Delivery Boy” stood in for an absent celebrity. He received two awards from the Writers Guild of America for his work on The Muppet Show. He also made a brief appearance as a police driver in The Pink Panther Strikes Again in 1976, opposite Peter Sellers. 1976 also saw the inception, at the Science Fiction Theatre of Liverpool, of the nine-hour stage play Illuminatus, which Langham co-wrote with Ken Campbell. In 1977 the production transferred to the Cottesloe Theatre, London, where he took the part of “George Dorn”, giving a performance which Peter Hall found “extremely impressive”.

Langham was part of the original cast for the pilot for Not the Nine O’Clock News in 1979, written by Richard Curtis. The show was positioned as a comedy series which was neither Monty Python’s Flying Circus nor The Two Ronnies. Even after the original pilot was pulled from the schedules, Langham was retained for the first full series, billed equally with the then-unknown Mel Smith, Pamela Stephenson, and Rowan Atkinson. The first series did not rate as well as hoped, however, and it was felt that Langham was “too independent a spirit.” Langham took a part in Monty Python’s Life of Brian as a centurion, against the reaction to which Curtis had written a skit of the debate between John Cleese and Malcolm Muggeridge. Langham was upset at the inclusion of the sketch, which gave the team and producer John Lloyd the excuse for his replacement by support player Griff Rhys Jones. Langham did not learn of the switch until the last day of filming when he heard the crew discussing the second series. The show only achieved cult status during its later series and, in subsequent compilation repeats, most of Langham’s contributions have been cut, giving the impression that he was never a main cast member.

Also in 1979, Langham played Arthur Dent in the first professional stage version of The Hitchhiker’s Guide to the Galaxy, directed by Ken Campbell. He later returned to Hitchhiker’s, appearing as Prak in Above The Title Productions’ Tertiary Phase radio series in 2004.

Langham went on to appear on Smith and Jones’ own programme, Alas Smith and Jones, playing an ineffectual panel show host. This character apparently inspired John Morton to create the character of Roy Mallard, who was later to feature in his show People Like Us; Mallard was played both on radio and (offscreen) on television by Langham. Langham also played a fly-on-the-wall documentary interviewer very similar to Roy Mallard in Happy Families in 1985.

Langham narrated the 1984 radio series The History of Rock with Chris Langham, in which Langham gave a comedic and somewhat fictitious account of the history of rock music. On 14 November 1985, Langham appeared as the narrator/reporter in “Roxanne”, episode five of the BBC situation comedy Happy Families, written by Ben Elton. In 1992, he appeared in the film Carry On Columbus.

In addition to several one-man shows, Langham counts among his stage credits Les Misérables, in which he played Thénardier in 1996; Crazy for You, for which he received an Olivier nomination; The Way of the World, The Nerd and The Pirates of Penzance. He created the comic role of the Assassin in Blondel (co-starring Paul Nicholas; by Tim Rice and Stephen Oliver), and appears on the original cast album.

Langham had paid with his credit card for access to a site entitled “European Lolita Sex” in 1999. On the evening that the public was made aware of the scope of Operation Ore, Langham had contacted police to report his “concern” about spam emails, with links to paedophile sites, which he said he was receiving. The prosecution said that he had contacted police because he had “panicked” and “wanted to give the impression of being a good citizen”.

Langham wrote the BBC One sitcom Kiss Me Kate, in which he appeared alongside Caroline Quentin and Amanda Holden. In 2002 he wrote and starred in Bradford in My Dreams, an adaptation of a short story by Lawrence Block for the BBC. On Radio 4 he narrated the series The Rapid Eye Movement, which starred Martin Freeman as Chester Bennington, in whose head the entire series took place. In 2003 he directed the BBC TV comedy series Posh Nosh.

In 2003 and 2005, respectively, he portrayed the authors George Orwell and John Wyndham in the BBC docudrama George Orwell – A Life In Pictures and the BBC Four documentary John Wyndham: the Invisible Man of Science Fiction. He also appeared in the radio magazine satire The Sunday Format.

He starred alongside co-writer Paul Whitehouse in Help on BBC Two in 2005, where he also appeared in the Armando Iannucci comedy The Thick of It in the same year. Langham was named Best Comedy Actor in the 2005 British Comedy Awards and won the 2006 BAFTA Best Comedy Performance award for his role in The Thick Of It. In November 2005 Langham wrote and starred in ITV pilot Seven Second Delay.

On 29 November 2005, Langham was arrested by Kent Police in connection with Operation Ore, a British police operation into credit card customers paying to access indecent and abusive images of children on the internet. The arrest was first reported in the press on 16 December 2005, in response to which Langham’s lawyer read a statement in which he said that he was innocent, and pointed out that he had not been charged. On 11 May 2006, he was charged with 15 counts of “making indecent images” (a legal term meaning to download and store indecent images as distinct from the act of photography) of children.

On 2 August 2007, Langham was found guilty on charges of possessing child pornography. He was sentenced to 10 months in prison and was placed on the sexual offenders register for 10 years. Before sentencing, the judge said that “some of the children viewed are clearly prepubescent… The worst video was 15 minutes long and it showed in quite graphic detail the sadistic brutalisation of an eight-year-old girl in the UK, with some serious sexual offences against her”.

He was released on 14 November 2007 after his sentence was reduced to six months on appeal. Dame Heather Steel, who gave the decision said that the court viewed Langham’s explanation that he viewed the child porn for research as “highly improbable” but could not actually reject it, although he was still guilty of encouraging “despicable acts” through downloading the pornography. On his release, Langham stated, “My life has been ruined but my conscience is clear” and complained that the media “completely ignored” the court’s “acceptance based upon all the evidence and expert opinion that I have no sexual interest in children”. A counter to his claims was provided by Detective Superintendent Paul Fotheringham of Kent Police, who told journalists after the trial in 2007, “Langham doesn’t like the label, but I am satisfied that he is a paedophile”.

A few days after his release from prison in 2008, Langham was interviewed by celebrity psychologist Pamela Connolly, with whom he had worked on Not the Nine O’Clock News, for her UK television series Shrink Rap, where he discussed being abused as an eight-year-old child, events which he said led to his trial and conviction. The interview was broadcast on More4 on 15 January 2008. Langham was also invited to make a speech in front of the Oxford Union on 29 May 2008 but the invitation was then withdrawn.

In 2011, in his first screen appearance after his release, he was cast as the lead in Black Pond, a low-budget British film directed by Tom Kingsley and Will Sharpe. In an interview with The Guardian in September 2011, Langham stated that many people had suggested to him that he should work again but no one wanted to employ him. Reviewing his performance in Black Pond positively, The Independent commented, “whether it will rehabilitate him among casting agents and comedy show commissioners is another question”. The “Kino Digital” cinema in Hawkhurst had a screening of the film on 11 December 2011. Afterwards, Langham, who lived nearby, held a brief question-and-answer session to help promote the film.

In 2012, he appeared with Billy Murray, Leslie Grantham and Crissy Rock in Richard John Taylor’s film drama Acceptance.