Who is Morgan McSweeney? The powermaker who projected Keir Starmer into No10 and is despised by Labour backbenchers

He came under huge scrutiny to leave his post after the extent of Mandelson's relationship with convicted sex offender Jeffrey Epstein was revealed.

Emails released by the US Department of Justice appear to show the disgraced Labour peer leaking highly sensitive Government information to Epstein during the 2008 financial crash.

Announcing his resignation, Mr McSweeney said he takes "full responsibility" for his advice to appoint the former Business Secretary in 2024.

His resignation prompted a passionate and emotional thank you message from the Prime Minister.

"It’s been an honour working with Morgan McSweeney for many years," Sir Keir said. "He turned our party around after one of its worst ever defeats and played a central role running our election campaign.

"It is largely thanks to his dedication, loyalty and leadership that we won a landslide majority and have the chance to change the country.

"Having worked closely with Morgan in opposition and in government, I have seen every day his commitment to the Labour Party and to our country. Our party and I owe him a debt of gratitude, and I thank him for his service."

But who really is Morgan McSweeney, the mind behind Sir Keir's rise to power?

After moving to the UK from his native Ireland in 1994, Mr McSweeney spent time in Israel before studying marketing and politics at Middlesex University.

He joined the Labour Party in 1997.

He worked in the party's attack and rebuttal unit, before being dispatched to campaign for marginal seats during the 2005 General Election.

Shortly after Tony Blair was re-elected for the third time, Mr McSweeney worked under now-Communities Secretary Steve Reed and gained a reputation for his organisation.

He was later appointed Mr Reed's Chief of Staff in Lambeth Council, after a failed attempt to become councillor in Sutton in 2006.

Between 2008 and 2010, he grew his reputation further by aiding successful elections and developing communication strategies across 17 wards in Barking and Dagenham. He was branded as "the real unsung hero of the whole thing".

He is also a senior figure on think tank Labour Together. After becoming director in 2017, he joined ranks with the likes of current Culture Secretary Lisa Nandy, Jon Cruddas, and Mr Reed. He later faced criticism in his role due to financial irregularities.

Later that year, in the Party, he sought to replace Jeremy Corbyn as Labour leader with another candidate, in an attempt to shift the party "from the hard left" and "build a sustainable winning electoral coalition".

He then led Sir Keir's successful leadership campaign in 2020. He was initially appointed as Chief of Staff, but after a poor performance in the Chesham and Amersham by-election in 2021, he was moved to a strategic role in office. He is said to have remained a key adviser.

Mr McSweeney was then appointed Director of Strategies during Sir Keir's General Election campaign, before being appointed the shared role of Head of Political Strategy.

After then-Chief of Staff Sue Gray resigned from her role, Mr McSweeney was re-appointed as the PM's Chief of Staff in October 2024.

But his tenure as Sir Keir's chief aide came crashing down after his influence on the decision to appoint Mandelson as US ambassador.

Mr McSweeney is seen as a close ally of the disgraced former ambassador and considered the driving force behind his appointment.

He is alleged to have had knowledge on Mandelson's continued relationship with the paedophile Epstein, even after his child sex conviction.