Around this time Bennett often found himself playing vicars and claims that as an adolescent he assumed he would grow up to be a Church of England clergyman, for no better reason than that he looked like one.
Bennett's first stage play Forty Years On, directed by Patrick Garland, was produced in 1968. Many television, stage and radio plays followed, with screenplays, short stories, novellas, a large body of non-fictional prose, and broadcasting and many appearances as an actor.
Bennett's distinctive, expressive voice and the sharp humour and humanity of his writing have made his readings of his work very popular, especially the autobiographical writings.
Many of Bennett's characters are unfortunate and downtrodden. Life has brought them to an impasse or else passed them by. In many cases they have met with disappointment in the realm of sex and intimate relationships, largely through tentativeness and a failure to connect with others.
Despite a long history with both the National Theatre and the BBC, Bennett never writes on commission, saying "I don't work on commission, I just do it on spec. If people don't want it then it's too bad."
Bennett is both unsparing and compassionate in laying bare his characters' frailties. This can be seen in his television plays for LWT from the early 1970s through to his work for the BBC in the early 1980s. His many works for television include his first play for the medium, A Day Out in 1972, A Little Outing in 1977, Intensive Care in 1982, An Englishman Abroad in 1983, and A Question of Attribution in 1991. But perhaps his most famous screen work is the 1987 Talking Heads series of monologues for television which were later performed at the Comedy Theatre in London in 1992. This was a sextet of poignantly comic pieces, each depicting several stages in the character's decline from an initial state of denial or ignorance of their predicament, through a slow realisation of the hopelessness of their situation, progressing to a bleak or ambiguous conclusion. A second set of six Talking Heads followed a decade later, which was darker and more disturbing.
In his 2005 prose collection Untold Stories, Bennett has written candidly and movingly of the mental illness that his mother and other family members suffered. Much of his work draws on his Leeds background and while he is celebrated for his acute observations of a particular type of northern speech ("It'll take more than Dairy Box to banish memories of Pearl Harbour"), the range and daring of his work is often undervalued. His television play The Old Crowd includes shots of the director and technical crew.
He wrote The Lady in the Van based on his experiences with an eccentric woman called Miss Shepherd, who lived on Bennett's driveway in a series of dilapidated vans for more than fifteen years. It was first published in 1989 as an essay in the London Review of Books. In 1990 he published it in book form. In 1999 he adapted it into a stage play, which starred Maggie Smith and was directed by Nicholas Hytner. The stage play includes two characters named Alan Bennett. On 21 February 2009 it was broadcast as a radio play on BBC Radio 4, with Maggie Smith reprising her role and Alan Bennett playing himself. He adapted the story again for a 2015 film, with Maggie Smith reprising her role again, and Nicholas Hytner directing again. In the film Alex Jennings plays the two versions of Bennett, although Alan Bennett appears in a cameo at the very end of the film.
Bennett's play People opened at the National Theatre in October 2012. In December that year, Cocktail Sticks, an autobiographical play by Bennett, premièred at the National Theatre as part of a double bill with the monologue Hymn. The production was directed by Bennett's long-term collaborator Nicholas Hytner. It was well-received, and transferred to the Duchess Theatre in the West End of London, being subsequently adapted for radio broadcast by BBC Radio 4.
In July 2018, Allelujah!, a comic drama by Bennett about an NHS hospital threatened with closure, opened at London's Bridge Theatre to critical acclaim.
In September 2005, Bennett revealed that, in 1997, he had undergone treatment for colorectal cancer, and described the illness as a "bore". His chances of survival were given as being "much less" than 50% and surgeons had told him they removed a "rock-bun" sized tumour. He began Untold Stories (published 2005) thinking it would be published posthumously, but his cancer went into remission.
In the autobiographical sketches which form a large part of the book Bennett wrote openly for the first time about his bisexuality. Previously Bennett had referred to questions about his sexuality as like asking a man who has just crawled across the Sahara desert to choose between Perrier or Malvern mineral water.
In October 2008, Bennett announced that he was donating his entire archive of working papers, unpublished manuscripts, diaries and books to the Bodleian Library, stating that it was a gesture of thanks repaying a debt he felt he owed to the British welfare state that had given him educational opportunities which his humble family background would otherwise never have afforded.
In September 2015, Bennett endorsed Jeremy Corbyn's campaign in the Labour Party leadership election. He said: "I think Jeremy Corbyn has given things a good kick in the pants and the fact that he has done so well shows that people are concerned about these issues. The Government would have you think that nobody is concerned about these things, but they are." In the October after Corbyn's election victory he said: "I approve of him. If only because it brings Labour back to what they ought to be thinking about."
Following the death of Jonathan Miller on 27 November 2019, he became the only surviving member of the original Beyond The Fringe quartet which had also included Peter Cook and Dudley Moore.
Bennett was made an Honorary Fellow of Exeter College, Oxford, in 1987. He was also awarded a D.Litt by the University of Leeds in 1990 and an honorary doctorate from Kingston University in 1996. In 1998 he refused an honorary doctorate from Oxford University, in protest at its acceptance of funding for a chair from press baron Rupert Murdoch. He also declined a CBE in 1988 and a knighthood in 1996. He has stated that, although he is not a republican, he would never wish to be knighted, saying it would be a bit like having to wear a suit for the rest of his life. Bennett earned Honorary Membership of The Coterie in the 2007 membership list.
In December 2011 Bennett returned to Lawnswood School, nearly 60 years after he left, to unveil the renamed Alan Bennett Library. He said he "loosely" based The History Boys on his experiences at the school and his admission to Oxford. Lawnswood School dedicated its library to the writer after he emerged as a vocal campaigner against public library cuts. Plans to shut local libraries were "wrong and very short-sighted", Bennett said, adding: "We're impoverishing young people."