Brown was born in Hawkhurst, Kent, and brought up in nearby Tunbridge Wells, attending Tunbridge Wells Grammar School for Boys before studying at the University of Manchester. After graduating, he worked in advertising for Procter & Gamble, but in 1978 he moved to become the legal adviser to the Northern Region of the GMBATU, later GMB, based in Newcastle upon Tyne.

In 1980, Brown was elected to Newcastle City Council, representing the Walker ward.

When Mike Thomas, the sitting Labour Member of Parliament (MP) for Newcastle upon Tyne East, defected to the SDP, Brown was chosen as the new Labour Party candidate for the seat, easily retaining it for Labour at the 1983 general election. He joined Labour’s front bench in 1985 as a spokesman on Legal Affairs; from 1988 he was a Treasury spokesman and from 1994 he shadowed Health.

Originally elected to the Commons in the same year as Gordon Brown and Tony Blair, Brown was initially close to both men, but over time became his namesake Brown’s staunchest ally, though the two are unrelated. In the 1994 Labour leadership election he acted as Brown’s unofficial campaign manager, and according to Gordon Brown’s biographer Paul Routledge, advised against him pulling out of the contest in Blair’s favour.

In 1995, he was appointed Deputy Chief Whip and played a central role in the close Parliament in trying to defeat the Conservatives. After Labour’s election victory in 1997, he was appointed Chief Whip, but stayed there only for just over a year, to then be moved to the Ministry of Agriculture, Fisheries and Food in during Tony Blair’s first ministerial shuffle in July 1998. This change, which followed the publication of the Routledge biography earlier that year, was widely seen as a demotion, and ascribed to his close connection with Brown.

His tenure at MAFF saw several animal health crises ending with the 2001 foot-and-mouth outbreak. Brown’s handling of the outbreak, which some in the media and politics used to attack the government, was criticised, though throughout he maintained the support of the farming and food industries and the veterinary profession. Suggestions that a vaccination strategy should have been practised in preference to the culling of hundreds of thousands of animals, made with the benefit of hindsight, did not help his cause, and he was demoted out to be the Minister of Work, with non-voting Cabinet rank, at the Department for Work and Pensions after the general election of 2001. In June 2003, he was dropped from the Government altogether.

In 2004, he was one of the organisers of a rebellion over the government’s proposals for student finance, but hours before the vote announced that he had received concessions from the Government and would now support it. It was suspected that the Chancellor had ordered him to back down, but the affair cost him some credibility.

Brown was closely allied to Gordon Brown. On 29 June 2007, Gordon Brown as Prime Minister, appointed Nick Brown as the new Deputy Chief Whip and Minister for the North East of England.

In 2009, Brown was appointed to investigate the legitimacy of expense claims by Labour MPs between 2004 and 2008. According to The Daily Telegraph in this period Brown himself claimed a total of £87,708 for his constituency home.

On 29 January 2010, during the News of the World phone hacking affair, Brown said that his landline may have been bugged in 1998, around the time of his outing. He was also contacted by an undisclosed police force in the West of England in 2003, who told him that they were pursuing a phone-tapping prosecution and he was one of those who may have been targeted. The case collapsed when it reached court and full details of the allegations were never disclosed. Brown said that: “Given that it was near [Prince Charles’ home] Highgrove, my assumption was that this might involve the Royal Family. But I was never explicitly told that.”

On 29 September 2010, newly elected Labour Party leader Ed Miliband asked Brown to stand down as Chief Whip due to the need for a “break from the past”.

In 2014, Brown publicly opposed his party’s proposal to scrap the position of Police and Crime Commissioner (PCC), citing the effectiveness of the three PCCs in the North East of England at the time.

On 6 October 2016, Brown was re-appointed Labour Chief Whip, under Jeremy Corbyn, and he went on to play an important role in the Parliamentary debates and votes over Brexit during 2018 and 2019. He played in key role in inflicting the largest ever defeat upon a government in British history.

Brown was reappointed by Keir Starmer after the latter’s victory in the 2020 Labour Party leadership election. This reappointment means that Brown is the only person to have held the job three times, as well as under six different leaders (Blair, Brown, Harman, briefly Miliband, Corbyn and Starmer) and in four different decades.