Early political career: 1980–1997

In 1980, Brown was elected to Newcastle City Council as a Labour councillor, representing the Walker ward.

Brown was chosen as the new Labour Party candidate for the parliamentary seat after Mike Thomas, the Labour Member of Parliament (MP) for Newcastle upon Tyne East, defected to the SDP. Brown easily retained the seat for Labour at the 1983 general election. 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.

Brown was first appointed to Labour's frontbench team in 1985 as a shadow solicitor general. In 1988, he was moved to the position of Treasury spokesperson before briefly becoming shadow spokesperson for health between 1994 and 1995.

In the 1994 Labour leadership election, he supported Gordon Brown and acted as his unofficial campaign manager and, according to biographer Paul Routledge, advised against his withdrawing from the contest in Blair's favour.

In 1995, Brown was appointed as Deputy Chief Whip in the House of Commons and played a central role in Parliament in trying to defeat the Conservative government's parliamentary agenda.

Government: 1997–2010

Following Labour's election victory in 1997, he was appointed as Government Chief Whip in the House of Commons, but stayed there only for just over a year, to then be moved to the Ministry of Agriculture, Fisheries and Food in 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 Gordon Brown.

His tenure as the Minister of Agriculture, Fisheries and Food saw several animal health crises, ending with the 2001 foot-and-mouth outbreak. Brown's handling of the outbreak was criticised by some and used to attack the government, though his handling of the crisis maintained the support of the farming and food industries and the veterinary profession throughout the crisis. 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 to Minister of State for Work, with non-voting Cabinet rank, 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 backbench rebellion against the government's proposals for the introduction of tuition fees, but hours before the vote announced that he had received significant concessions from the Government and would now support it. Some suspected that the Chancellor had placed considerable pressure on him to back down and the affair cost Brown some credibility.

On 29 June 2007, Gordon Brown became Prime Minister and immediately appointed Nick Brown as the Regional Minister for the North East and simultaneously as the new Deputy Chief Whip.

Following a government reshuffle in 2008, Gordon Brown returned Nick Brown to his original government position of Government Chief Whip, whilst retaining his position as Minister for the North East.

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.^[3]

Brown's mortgage interest repayments for 2007–8 totalled £6,600, but he also claimed a total of £23,068, just £15 below the maximum allowable amount for the year. The claim included £4,800 for food – the maximum allowable amount – £2,880 for repairs and insurance, £2,880 for services, £897.65 for cleaning, £1,640 for phones and £1,810 for utilities. Brown, however, has said that he saved the taxpayer a considerable amount of money by turning down a Government car and driver upon being made Chief Whip, the annual cost of which would have been around £100,000.^[4]

Opposition: 2010–present

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".^[5]

On 29 January 2011, 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 being outed.^[6] 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."^[6]

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 North East England at the time.^[7]

Ahead of the 2016 EU membership referendum, Brown stated he supported remaining in the European Union.^{[citation needed]}

On 6 October 2016, Brown was appointed by Jeremy Corbyn as Chief Whip of the Labour Party, and thus became Opposition Chief Whip in the House of Commons.^[8]

Brown was reappointed as Labour Chief Whip by Sir Keir Starmer after the latter's victory in the 2020 Labour Party leadership election.^[9] This reappointment meant that Brown was the only person to have held the role for three non-consecutive terms, as well as under six different leaders (Blair, Brown, Harman, briefly Miliband, Corbyn and Starmer) across four decades. Brown left the role of Chief Whip for the third time as a result of Starmer's Shadow Cabinet reshuffle in May 2021. On 26 May 2021, Brown returned as chair of the Finance Committee.^[10]

In September 2022, Brown was suspended from the Labour Party following allegations concerning an event 25 years previously, details of which were not made public.^[11][12] On 12 December 2023, he resigned from the Labour Party in protest at the unresolved disciplinary process. He also announced that he would not be contesting the next election.^[11]