2015 Labour Party leadership election (UK)

The 2015 Labour Party leadership election was triggered by the resignation of Ed Miliband as Leader of the Labour Party on 8 May 2015, following the party's defeat at the 2015 general election. Harriet Harman, the Deputy Leader, became Acting Leader but announced that she would stand down following the leadership election. It was won by Jeremy Corbyn in the first round. In the 2015 Labour Party deputy leadership election, which was run simultaneously, Tom Watson was elected to succeed Harman as deputy leader.

Four candidates were successfully nominated to stand in the election: Andy Burnham, Yvette Cooper, Jeremy Corbyn, and Liz Kendall. The voting process began on Friday 14 August 2015 and closed on Thursday 10 September 2015, and the results were announced on Saturday 12 September 2015. Voting was by Labour Party members and registered and affiliated supporters, using the alternative vote system.

Support for Corbyn, who entered the race as a dark horse candidate, and the release of opinion polls which showed him leading the race, led to high-profile interventions by a number of prominent Labour figures including Gordon Brown, Tony Blair, Jack Straw, David Miliband, and Alastair Campbell, among others, many of whom argued that Corbyn's election as leader would leave the party unelectable.

Despite these interventions, Corbyn was elected in the first round receiving 59.5% of the votes, winning in all three sections of the ballot. Less than a year later, a leadership challenge saw another leadership election, where Corbyn again won, with an increased share of the vote.