Informal campaigning had been ongoing ever since Tony Blair's original announcement in 2004 that he would not be fighting a fourth general election as leader. Pressure for a timetable eventually led him to announce on 7 September 2006 that he would step down within a year. Labour's National Executive Committee (NEC) met on 13 May 2007 to decide a timetable. Nominations opened on 14 May and closed at 12:30 UTC+1 on 17 May 2007.
Blair said he expected Gordon Brown to succeed him, and that Brown 'would make an excellent Prime Minister'. When nominations for the leadership elections opened, Blair was one of those nominating Brown. From the start most observers considered Brown the overwhelming favourite to succeed Blair; John McDonnell, his only challenger, failed to secure enough nominations in order to get onto the ballot and conceded defeat to Gordon Brown.
John McDonnell and Gordon Brown were the only candidates as the election process began with the nominations round. In order to secure a place on the ballot paper, candidates needed to submit their nominations to the NEC by 17 May supported by at least 12.5% of Labour MPs (45 Labour MPs, including the candidate themselves). Gordon Brown, the only successfully nominated candidate, was declared leader at a special Labour conference on 24 June 2007.
John McDonnell, chair of the Socialist Campaign Group, pledged to merge Old Labour and New Labour into what he calls Real Labour and "save the Labour government from itself". He was hoping to get the backing of all those who had been backing Michael Meacher, but did not do so; with 29 nominations he was 16 short of the minimum required number and was not successfully nominated.
Charles Clarke, former Home Secretary, had insisted he would stand if David Miliband did not, but later softened his position with praise for Brown and saying that the Labour Party didn't have the appetite for a contest. He indicated that he would like to serve in a future Labour Cabinet; however, he was not offered any position, and lost his seat in the subsequent general election.
Michael Meacher, former Minister of State for the Environment, was a candidate but had to withdraw after failing to get enough nominations. On 27 April 2007, McDonnell and Meacher announced that whichever of them had the support of fewer Labour MPs at the point of Tony Blair's resignation would withdraw from the campaign and support the other. On 10 May 2007 they delayed their announcement because "levels of support for each were too close to call". He gave his support to John McDonnell on 14 May 2007, but not all his supporters switched allegiance.
Alan Milburn ruled out standing for the Labour leadership on 11 May 2007, but previously had refused to rule it out.
John Reid, Home Secretary, had said he would not reveal whether he would stand or not until there was a vacancy, but on 6 May announced he would be voting for Brown and had decided to leave the Cabinet along with Blair.