He has been the Member of Parliament (MP) for Hayes and Harlington since 1997, representing the Labour Party until the whip was withdrawn and his suspension on 23 July 2024 as a result of voting to scrap the two child benefit cap.

He stood for the position of Labour Party leader following Tony Blair's resignation in 2007, but failed to reach the required number of nominations.

[3] He was a candidate for the party leadership again in 2010 following Gordon Brown's resignation after Labour's electoral defeat,[4] but withdrew in favour of Diane Abbott, feeling that he would be unable to secure enough nominations.

[8] His father, Bob, was a docker who also served as a sergeant in the Sherwood Foresters during World War II, whilst his mother Elsie worked as a cleaner.

[11] McDonnell received a Local Authority grant to attend St Joseph's College, Ipswich,[12] a Roman Catholic boarding fee-paying independent school for boys (now co-educational).

After marrying his first wife, he returned to A-level studies at night school at Burnley Technical College, and at the age of 23, he moved to Hayes in Greater London, attended Brunel University, and earned a bachelor's degree in government and politics.

[13][14] During this period, he helped his wife run a small children's home in Hayes, and was active on behalf of his local community and for National Union of Public Employees.

He became the GLC's chair of finance and deputy leader to Ken Livingstone, who described him as having an "absolute grasp for detail and every year he produced a balanced budget, no borrowing".

[17][18] In an interview with Ronan Bennett for The Guardian newspaper, McDonnell described his role during this time as being "to translate policies into concrete realities on the ground."

We set in train policies for which we were attacked from all sides but are now accepted as mainstream: large-scale investment in public services; raising the issue of Ireland and arguing for a dialogue for peace; equal opportunities; police accountability.

Having previously unsuccessfully contested Hampstead and Highgate in 1983, McDonnell fought for his home constituency of Hayes and Harlington at the 1992 general election, but lost by 53 votes, after three recounts, to the Conservative incumbent, Terry Dicks.

He opposed New Labour policies of the Iraq War, foundation hospitals, student top-up fees, trust schools and anti-terror laws.

[22] In October 2006, McDonnell was one of 12 Labour MPs to back Plaid Cymru and the Scottish National Party's call for a parliamentary inquiry into the war in Iraq.

In May 2003, he made controversial comments about the Provisional Irish Republican Army (IRA), saying:It's about time we started honouring those people involved in the armed struggle.

The future for achieving the nationalists' goals is through the political process and in particular through the Northern Ireland Assembly elections ... Irish republicans have to face the fact that the use of violence has resulted in unforgivable atrocities.

The Deptford Mercury asserted at the time that McDonnell had suggested there was a role for "the ballot, the bullet and the bomb" in achieving a United Ireland, and joked about "kneecapping" the "gutless wimp" Labour councillors who had declined to join the meeting.

"[27] In his study at Hayes, McDonnell has a plaque presented to him by Gerry Kelly dedicated to the "H-Block Martyrs 1981", referring to those who died during the 1981 Irish hunger strike.

[44] In 2006, during the parliamentary debate on the Budget Resolutions, McDonnell warned against public-private finance initiatives (PFIs), calling for an inquiry:There are numerous examples.

I remember fighting for four years, in almost a solitary capacity, to secure the passage of the City of London (Ward Elections) Bill at a time when we were pressing for regulation.

McDonnell picked up the ceremonial mace and placed it down on an empty bench in the Commons while shouting that the lack of a vote on the third runway was "a disgrace to the democracy of this country.

[55] In a YouGov opinion poll of more than 1,100 Labour Party members asking their preferred choice in the leadership contest, McDonnell received 9% support, and was ranked second to Chancellor Gordon Brown, who led with 80% of the vote.

This will include the introduction of an effective regulatory regime for our banks and financial sector; a full-blown Glass-Steagall system to separate day-to-day and investment banking; legislation to replace short-term shareholder value with long-term sustainable economic and social responsibilities as the prime objective of companies; radical reform of the failed auditing regime; the extension of a wider range of forms of company and enterprise ownership and control including public, co-operative and stakeholder ownership; and the introduction of a financial transactions tax to fund the rebalancing of our economy towards production and manufacturing.

"[67] However, he reversed that call in October, citing his trip to visit former steelworkers at a recently closed plant in Redcar as the reason for not wanting to be associated with supporting government cuts.

[71][72] McDonnell has explored ideas surrounding "alternative models of ownership", publishing a report on the subject in June 2017 and hosting a discussion conference in London in February 2018.

[74] During his response to the 2015 Autumn Statement in which he accused George Osborne of "sheer economic illiteracy", McDonnell highlighted that the government was "selling off at least £5 billion worth of our own assets" to foreign investors, emphasising China.

[75] To make this point he quoted from a copy of Chairman Mao Zedong's Little Red Book and then threw it across the despatch box towards the Conservative front bench.

[79] The use of the word "murder" was questioned by some of his colleagues as well as the Conservative Party, with Jim Fitzpatrick, leader of the All-Party Parliamentary Group on Fire Safety suggesting it was "premature" to draw conclusions about what caused the deaths.

[92] On 24 February 2022, following the 2022 Russian invasion of Ukraine, McDonnell was one of 11 Labour MPs threatened with losing the party whip after they signed a statement by the Stop the War Coalition which questioned the legitimacy of NATO and accused the military alliance of "eastward expansion".

[96] In July 2024, McDonnell campaigned on and voted for the scrapping of the two child benefit cap which he opposed in 2015 when it was introduced under the Conservatives, defying the Labour whip.

[106] On 19 January 2025, McDonnell, alongside Jeremy Corbyn, agreed to be interviewed under caution by police following a pro-Palestinian rally in central London.