Bell is the son of author-farmer Adrian Bell, compiler of the first ever Times crossword. He is the brother of literary translator, Anthea Bell OBE and the uncle of Oliver Kamm, now a Times leader writer, who served as his political adviser during his term as a Member of Parliament (MP).
He was educated at The Leys School in Cambridge and King's College, Cambridge, where he achieved a First Class Honours Degree in English. He served on the committee of Cambridge University Liberal Club, including a term as Publicity Officer. He failed to obtain a commission during his two-year national service and served out his time as an acting corporal in the Suffolk Regiment serving in Cyprus during the emergency.
Martin Bell joined the BBC as a reporter in Norwich in 1962 as a 24-year-old, following his graduation. He moved to London three years later, beginning a distinguished career as a foreign affairs correspondent with his first assignment in Ghana. Over the next thirty years, he covered eleven conflicts and reported from eighty countries, making his name with reports from wars and conflicts in Vietnam, Middle East, Nigeria, Angola, and in Northern Ireland (during the "Troubles").
His roles at the BBC included diplomatic correspondent (1977–78), chief Washington correspondent (1978–89), and Berlin correspondent (1989–94).
He won the Royal Television Society's Reporter of the Year award in 1977 and 1993, and was appointed an Officer of the Order of the British Empire (OBE) in 1992. That same year, while covering the war in Bosnia, Bell was seriously wounded by shrapnel while recording a report in Sarajevo.
He remained an official BBC correspondent, although from the mid-1990s he filed relatively few reports, and became disillusioned with the BBC. He was unimpressed by the BBC's introduction of a 24-hour news channel (BBC News 24) and what he described as the increasing "Murdochisation" of BBC News.
In 1997, twenty-four days before that year's British General Election, Martin Bell announced that he was leaving the BBC to stand as an independent candidate in the Tatton constituency in Cheshire. Tatton was one of the safest Conservative seats in the country, where the sitting Conservative Member of Parliament, Neil Hamilton, was embroiled in "sleaze" allegations. The Labour and Liberal Democrat parties withdrew their candidates in Bell's favour in a plan masterminded by Alastair Campbell, Tony Blair's press secretary.
Hamilton was trounced, and Bell was elected an MP with a majority of 11,077 votes – overturning a Conservative majority of over 22,000 – and thus became the first successful independent parliamentary candidate since 1951.
He did not often speak in the House of Commons, and when he did, it was mostly on matters of British policy in the former Yugoslavia and the Third World. Although Bell voted with the Labour government of Tony Blair on many issues, on a few others, such as reducing the homosexual age of consent and banning fox hunting, he voted with the Conservatives. On 12 November 1997, he was cheered from the Conservative benches when he asked Blair about the Bernie Ecclestone affair, "Does the Prime Minister agree that the perception of wrong-doing can be as damaging to public confidence as the wrong-doing itself? Have we slain one dragon only to have another take its place, with a red rose in its mouth?".
He was urged by large numbers of his Tatton constituents to stand again in the 2001 general election. Bell said that the only thing which could make him change his mind would be Neil Hamilton being re-selected by the Tatton Conservative Party as candidate for the next General Election. However, future Chancellor George Osborne was selected in March 1999, as Conservative party candidate for Tatton. Hamilton lost his libel case against Mohamed Al-Fayed in December 1999, ending any prospect of him making an immediate political comeback. Though he regretted making the pledge of saying he would only serve for one term, Bell stuck to his promise.
In 2001, Bell was nonetheless persuaded to stand as an independent candidate against another Conservative MP Eric Pickles in the "safe" Essex constituency of Brentwood and Ongar, where there were accusations that the local Conservative Association had been infiltrated by a Pentecostal church. In this election, Labour and the Liberal Democrats did not stand aside for him; However Bell still managed to come second and reduced the Conservative majority from 9,690 to just 2,821.
Having garnered nearly 32% of the votes and a strong second place, Bell announced his retirement from politics, saying that "winning one and losing one is not a bad record for an amateur".
The Channel 4 drama Mr White Goes to Westminster was loosely based on Bell's political career.
Bell was appointed UNICEF UK Ambassador for Humanitarian Emergencies in 2001, to work to improve the plight of children affected by conflict and natural disaster.
He made a brief return to television news in 2003 when he provided analysis of the Iraq invasion for ITN's Channel Five News. He compiled films from the daily video footage and drew on his experience to comment upon this material.
Bell reversed his previous decision and stood for the European Parliament in the June 2004 elections, but was ultimately unsuccessful as an independent candidate in the East of England region, winning only 6.2% of the vote.
Before the 2005 general election he became affiliated with the Independent Network to help promote independent candidates (its most prominent candidate being Reg Keys who fought against prime minister Tony Blair in the Sedgefield constituency).
In April 2006, Scottish National Party MP Angus MacNeil asked the Metropolitan Police to investigate whether any law had been broken in the Cash for Peerages scandal. Bell wrote jointly with MacNeil to Prime Minister Tony Blair calling for all appointments to the House of Lords to be suspended.
In May 2009, he came out in support of the Green Party in the weeks before the 2009 European elections, supporting the Green Party's 'Clean Campaigning' pledge in the wake of the scandal over MPs' expenses.
On 21 May 2009, he appeared on the special live edition of BBC's Question Time which was held in Salisbury in the midst of the political scandal surrounding MPs' expenses.
He announced that he was considering standing against a third Conservative MP, Sir Nicholas Winterton, the MP for Macclesfield in the 2010 General Election, but following the latter's announcement that he was not going to seek re-election, did not do so. He indicated that he might stand against Hazel Blears in Salford (the first sitting MP of a party other than the Conservative party against whom he expressed an interest in standing) although in the end he did not stand in any constituency.In Harm's Way (London, 1995, revised edition 1996) ISBN 0-14-025108-1
An Accidental MP (Viking, London, 2000, Penguin paperback 2001) ISBN 0-670-89231-9
Through Gates of Fire: a Journey into World Disorder (London, 2003, Phoenix paperback 2004) ISBN 0-7538-1786-1
The Truth That Sticks: New Labour's Breach of Trust (Icon Books, London, 2007) ISBN 1-84046-822-X
A Very British Revolution: The Expenses Scandal and How to Save Our Democracy (Icon Books, London, 2009) ISBN 978-1-84831-096-4
For Whom the Bell Tolls (Icon Books, London, 2011) ISBN 978-184831-691-1
The End of Empire (Pen & Sword, Barnsley, 2011) ISBN 978-1-47384-818-4
War and the Death of News (Oneworld, London, 2017) ISBN 978-1-78607-108-8