Local Labour organiser In 1997, motivated by backing for the
Good Friday Agreement, McSweeney joined the
Labour Party, and in 2001 he was hired to work as an intern receptionist and then in the party's attack and rebuttal unit in
Millbank, where he input data into
Peter Mandelson's "
Excalibur" database. also focusing on
patriotism and
crime as campaign points. Under his leadership, Labour Together worked on a strategy to remove
Jeremy Corbyn from the party leadership and to institute reforms to Labour Party processes to prevent the left wing of the party from subsequently regaining the leadership. In February 2026, it was reported that Labour Together paid the PR firm
APCO Worldwide to spy on journalists critical of Starmer. These included reporters from
The Sunday Times,
The Guardian and
Declassified UK. This had also previously been detailed in Paul Holden's book
The Fraud. As part of Labour Together's strategy to diminish the influence of the left, he had also worked to prevent the newly founded left-wing news website
The Canary from growing in popularity among Labour members, while building a close link between the mainstream centre-left newspaper
The Guardian and Labour Together.
Director of Campaigns In September 2021 McSweeney was appointed as Labour's
director of campaigns.
The Times has noted that "Those who question his authority inevitably find Starmer sides with McSweeney." McSweeney led preparations for the
2024 general election, McSweeney made contact with members of the US
Democratic Party and
Australian Labor Party, respectively
Neera Tanden and
Anthony Albanese, to discuss election tactics. He argued in a December 2023
shadow cabinet meeting that despite Labour's significant lead in national polls, six different elections from around the world were examples of leads reversing once campaigns began.
In government Head of political strategy Following Labour's victory in the 2024 general election on 4 July, McSweeney was appointed the head of political strategy alongside
Paul Ovenden. Some media reports suggested in August that McSweeney had come into some tension with Starmer's chief of staff
Sue Gray, with McSweeney being more politics-focused and Gray being governance-focused, both allegedly developing rival power centres within
10 Downing Street. McSweeney privately rejected the idea and insisted that he worked well with Gray.
Downing Street Chief of Staff Following the resignation of Sue Gray, McSweeney was appointed
Downing Street Chief of Staff on 6 October 2024.
Vidhya Alakeson and
Jill Cuthbertson were appointed as his deputies.
Briefings In November 2025, Starmer sought to draw a line under briefings by his allies that No 10 feared
Wes Streeting could launch a leadership coup. Starmer gathered staff to stress that briefings against cabinet ministers were "unacceptable" after apologising to Streeting. However, his spokesperson said that Starmer also accepted assurances that No 10 staff had not briefed against Streeting and that he stood by his chief of staff. Previously, McSweeney was accused of briefing against Gray.
Reputation McSweeney built a reputation as a Labour organiser, leading successful campaigns to win a majority on the
Lambeth London Borough Council and to defeat the far-right
British National Party in
Barking and Dagenham though his role and effectivness in relationship to this campaign and labour victory has been questioned . In September 2023,
New Statesman ranked McSweeney third on a list of the most influential left-wing figures in the UK and described him as Starmer's "most trusted aide". In February 2025, Bethany Dawson of
Politico Europe stated that McSweeney "is seen as a key protagonist in the rise of Prime Minister Keir Starmer."
James Ball of
The New European described McSweeney in May 2025 as "a core foot soldier in the internal resistance to Corbyn during his leadership, and was behind efforts to stamp out dissent once Starmer won," saying that he "has risen to an astonishing level of power and influence with the government, not least through the brutally effective removal of internal rivals." In October 2023,
The Times stated that "nobody without elected office wields as much power in British politics as McSweeney",
Jason Cowley of
New Statesman compared McSweeney to prominent Conservative Party adviser
Dominic Cummings, saying that both "continue to exert a special fascination," among observers of British politics.
Mandelson-Epstein friendship scandal and resignation In September 2025, when
Peter Mandelson was dismissed as ambassador to the United States after further revelations of his close friendship with child sex offender
Jeffrey Epstein, it was reported that McSweeney, who was known to be personally close to Mandelson, had been a "keen advocate" for Mandelson's appointment as ambassador despite his involvement with Epstein already being known, and despite concerns raised by the security services during the vetting process. Some Labour MPs were reportedly angry at McSweeney's influence, accusing him of promoting a
factional,
clique-driven style of politics, especially as allies of Starmer and McSweeney had recently been promoted during
a cabinet reshuffle in September 2025. In October 2025, McSweeney, who was then the Downing Street Chief of Staff, reported his government-issued phone stolen by a cyclist in Westminster. The incident gained significant attention in March 2026 following a parliamentary order for the government to release communications between McSweeney and Mandelson regarding the latter’s appointment as US ambassador. Critics, including Conservative opposition leader
Kemi Badenoch, have raised concerns about the timing of the theft, while Prime Minister Keir Starmer has dismissed suggestions of a "cover-up" as "far-fetched". To provide transparency, the Metropolitan Police released a transcript of McSweeney’s 999 call, which revealed he initially provided an incorrect street name, leading to the case being recorded in the wrong location and subsequently closed. The Met has since reopened the investigation to reassess evidence in the correct area. In February 2026, Starmer defended McSweeney, stating: "Morgan McSweeney is an essential part of my team. He helped me change the Labour party and win an election. Of course I have confidence in him. Whatever is slung across this Dispatch Box, I do not think it is right for the Cabinet Secretary to be denigrated in that way, or to suggest that he would be involved in a cover-up. There is the politics that comes over the Dispatch Boxes, but I honestly do not think it is right to impugn the Cabinet Secretary in that way."
Career after government On 8 February 2026, following increasing internal pressures, McSweeney resigned as Starmer's chief of staff. In a written statement, McSweeney took responsibility for the decision to appoint Mandelson, acknowledging it was wrong and had damaged the party and trust in politics. He stated that stepping aside was "the only honourable course". McSweeney expressed pride in the government's achievements, stating that his motivation was always to support a Labour government focused on ordinary people. He also highlighted the importance of remembering the victims of Epstein. Although he did not oversee vetting, he called for it to be fundamentally overhauled. He concluded by affirming his support for Starmer's mission. Starmer accepted McSweeney’s resignation and issued a statement expressing gratitude for his service. Starmer stated that he and the Labour Party owe McSweeney a "debt of gratitude" for his years of service. He credited McSweeney with a central role in the party's electoral success, including the
2024 landslide majority. Starmer praised McSweeney's "dedication, loyalty and leadership" and said it had been an honour to work with him. Following McSweeney's resignation,
The Guardian described the move as a significant political shake-up, highlighting increased scrutiny of Downing Street's vetting procedures. The resignation also prompted discussions within the Labour Party about improving internal oversight and accountability. His resignation led to
Tim Allan resigning as Director of Communications the following day.
Vidhya Alakeson and
Jill Cuthbertson were appointed by Starmer as McSweeney's acting successors. Scottish Labour Party leader
Anas Sarwar held a press conference in Glasgow to publicly call for Starmer to resign. In the immediate aftermath, senior Cabinet members including Deputy Prime Minister
David Lammy and Chancellor
Rachel Reeves rallied behind Starmer, emphasising his mandate and urging party unity. Addressing the Parliamentary Labour Party later that evening, Starmer remained defiant, stating he had "won every fight I've ever been in" and refused to walk away.
Parliamentary Inquiries In April 2026, McSweeney was called to give evidence to the
Foreign Affairs Select Committee on his role in Mandelson's security vetting. This followed former senior
Foreign Office civil servant
Olly Robbins alleging that the Prime Minister's office had a "dismissive" attitude towards the vetting process. McSweeney gave a statement to the committee apologising to the victims of
Epstein, and was probed by the members of the committee into his role in the appointment of Mandelson as US Ambassador. When referring to revelations including pictures of Mandelson and Epstein that appeared following the former's appointment as ambassador, he used the phrase "knife to my soul". He denied that
Mandelson was appointed because he was a "hero" or "mentor", and instead claimed his motivates had been in the national interest throughout the process. McSweeney also attended the Kyiv Security Conference in April 2026. The Sunday Times claimed that he was interested in how
artificial intelligence might shape
future elections in Ukraine. == Political positions and ideology ==