Dimbleby was born in Surrey, the son of the journalist and Second World War war correspondent Richard Dimbleby, by his marriage to Dilys Thomas, from Wales. His younger brother is Jonathan Dimbleby, also a television current affairs presenter. David Dimbleby was educated at two independent schools, the Glengorse School in Battle, East Sussex, and Charterhouse School in Godalming, Surrey, where he was a contemporary of the journalist Adam Raphael. The two younger Dimblebys both made their television débuts in the 1950s in the BBC's first holiday programme Passport, at a time when the whole family would visit resorts in Switzerland or Brittany. A holiday programme for the home countries, called No Passport, was also broadcast.
After learning French in Paris and Italian in Perugia, Dimbleby read Philosophy, Politics and Economics at Christ Church, Oxford and graduated with a third-class honours degree. While at Oxford he was President of the Christ Church JCR, a member of the Bullingdon Club – a socially exclusive student dining and drinking society – and also editor of the student magazine Isis.
Dimbleby joined the BBC as a news reporter in Bristol in the 1960s and has appeared in news programmes since 1962, early on co-presenting the televised version of the school quiz Top of the Form, and was a reporter on the BBC's coverage of the 1964 General Election with his father as linkman. Richard Dimbleby died the following year.
On 24 July 1967, Dimbleby was one of 70 signatories to The Times advertisement advocating the decriminalisation of cannabis use, which had been written by campaigner Stephen Abrams. An incident in 1969 led to Dimbleby, then freelance, being called in by the BBC's Director of Television. During President Richard Nixon's visit to Britain, a reference by Dimbleby to UK and US government heads' "'expensively hired" press secretaries "whose job is to disguise the truth" was given much attention by the British press.
He became involved in a number of projects that combined his established role as presenter and interviewer with documentary making. An early example of this was Yesterday's Men (1971), a film which the BBC recognises "ridiculed" the Labour opposition and led to a major conflict between the Corporation and the Labour Party; Dimbleby had his name removed from the credits because of the concessions that were made. In 1974, he became the presenter of Panorama, which had been presented by his father.
Dimbleby anchored the BBC's overnight coverage of the 1979 general election, and continued in this role for the following ten general elections. In addition to election coverage, he also hosts BBC Budget specials, and was a presenter of the BBC early evening weekday current affairs series Nationwide. During the same period (beginning in 1979), Dimbleby has also been the anchor for the BBC's European Elections results programmes and in 2008 and 2012 anchored the BBC's coverage of the US Election night.
Dimbleby was the main presenter of the BBC's political series This Week Next Week (1984–88), broadcast on Sunday early afternoons, as a competitor to ITV's established Weekend World series. This Week Next Week was replaced in 1988 by the On the Record, a political series presented until 1993 by his younger brother, Jonathan Dimbleby. Meanwhile, he continued to work in documentaries, including The White Tribe of Africa (1979), an award-winning four-part history of South Africa's Afrikaans community and the rise of apartheid, An Ocean Apart (1988), an examination of the history of Anglo-American relations, and Rebellion! (1999), a history of Britain's troubled relations with Zimbabwe.
By this time, Dimbleby was established as the anchor for the BBC's coverage of events of national importance, such as the State Opening of Parliament, the Trooping the Colour, the Remembrance Day service at the Cenotaph in Whitehall.
David Dimbleby has been chairman of Question Time since 1994. His involvement in the BBC's Thursday evening topical debate programme is the role in which he is now best known. One of the most memorable moments from Question Time was when Dimbleby accidentally referred to Robin Cook as "Robin Cock", to which Cook responded by jokingly referring to Dimbleby as "David Bumblebee".
In 1999, he opened BBC 2000 Today, the BBC's coverage of the millennium celebrations, from Greenwich, England. He commentated on the funerals of Diana, Princess of Wales in 1997, Queen Elizabeth the Queen Mother in 2002, and Margaret Thatcher in 2013, as well as the state visit of US President George W. Bush to Britain in 2003. In 2002, Dimbleby hosted the Golden Jubilee of Queen Elizabeth II coverage. A profile by Ben Summerskill for The Observer in 2001 quoted an unnamed former Cabinet Minister who had observed Dimbleby's career for many decades: "I suspect he has an almost medieval view, that the Queen governs through Parliament... There are a few quarrels among the subjects – over which he presides very capably – but they have very little to do with what Britain is really about." Dimbleby, though, has himself criticised what he sees as archaic elements of the State Opening of Parliament.
David Dimbleby was chairman of the Dimbleby Newspaper Group, former publishers of the Richmond and Twickenham Times, acquired by the Newsquest Media Group in 2001 for a reported £12 million.
There were reports in 2004 that Dimbleby was shortlisted for the Chairmanship of the BBC. However, the position was eventually awarded to Michael Grade. As early as 1987, he was a contender for the position of Director General of the BBC (losing out to Michael Checkland) and for the chairmanship in the Corporation's tumultuous period following 2001, which went to Gavyn Davies. He has instead remained, according to Mark Duguid for the BFI's screenonline website, best known for his "gravitas, journalistic integrity and consummate professionalism" and as "a paragon of impartiality" as a narrator and moderator, of British politics.
In 2005, he hosted a BBC One series, A Picture of Britain, celebrating British and Irish paintings, poetry, music, and landscapes. In June 2007 he wrote and presented a follow-up, the BBC series, How We Built Britain, in which he explored the history of British architecture by visiting a region of Britain and its historic buildings each week. David Dimbleby also presented a new series on BBC One, Seven Ages of Britain. In early editions of the programme, he looked at the Bayeux Tapestry and exhibits to do with Thomas Becket.
On 12 November 2009, Dimbleby missed his first Question Time in over 15 years, having been taken to hospital as a precaution after being briefly knocked out by a rearing bullock at his farm in Sussex.
Dimbleby hosted the third of three televised election debates featuring the leaders of the three main political parties held in the run up to the 2010 general election. On the night of the 2010 Election, Dimbleby hosted the BBC coverage, along with Jeremy Vine, Jeremy Paxman, Nick Robinson, and Emily Maitlis. Presenting from BBC Television Centre Studio 1, he was an anchor and involved commentary contributions, guest interviews, and introducing live outside broadcasts. In 2013, Dimbleby presented Britain and the Sea and a year later, he presented The European Union: In or Out. In 2015, Dimbleby hosted the first BBC General Election debate, in spite of the fact that neither David Cameron nor Nick Clegg took part.
Dimbleby hosted the EU referendum results show on BBC One, BBC News and BBC World News overnight on 23–24 June 2016, when the United Kingdom historically chose to leave the European Union in which he quoted to the country when the BBC released its forecast for a Leave win at 0440 BST:
On 20 April 2017, the BBC announced Dimbleby would host their coverage of the 2017 General Election despite having announced that the 2015 General Election would be his last.
Despite the brothers presenting election coverage on competing channels, when asked in an interview about rival ITV's plans to include a riverboat party with the likes of Kevin Spacey and Richard Branson in their broadcast, David Dimbleby commented "They've got Jonathan Dimbleby, what do they need Kevin Spacey for?"
Dimbleby has three children by his first wife, Josceline Dimbleby, a cookery writer: Liza, an artist; Henry, now a chef and co-founder of the healthy fast food chain Leon; and Kate, a jazz and folk singer. Henry Dimbleby had a brief television career in a 1984 BBC TV adaptation of Arthur Ransome's children's novels Coot Club and The Big Six; Swallows and Amazons Forever!. It was revealed by Jacob Rees-Mogg on the BBC Programme Question Time in December 2015 that Henry Dimbleby was his contemporary at Eton College.
In 2000, Dimbleby married Belinda Giles, a granddaughter of Herbrand Sackville, 9th Earl De La Warr with whom he has a son, Fred. Dimbleby lives in Polegate, East Sussex with a second home in Dartmouth, Devon. He is a supporter of Tranmere Rovers Football Club.
He was made an honorary graduate of the University of Essex in 2005, and is the President of the Institute for Citizenship. He is a current patron of St Wilfrid's Hospice, Eastbourne.