David Miliband has announced his intention to run for the leadership of the Labour Party.
Mr Miliband, 44, is supported by the Blairite faction of the party and Alan Johnson offered him his support earlier after saying he would not be standing for the role.
He said this afternoon that he hoped the race would be a “genuine, real contest” that would give credit to the party.
Mr Miliband said he intended to stand with a “deep sense of humility” and a “great, great passion” for Labour values.
He said: “I’m standing for the leadership because I believe I can lead Labour to rebuild itself as the great reforming champion of social and economic change in this country. We have achieved a great deal in government, but this is a new era: new dangers, new opportunities, new possibilities.
“No longer the party in government, we must be the party of real change right throughout the country. Deep renewal of our party, deep roots in our country, real engagement with its people.”
He added that he would formally launch his campaign in his South Shields constituency at the beginning of next week.
Gordon Brown resigned as party leader on Monday and resigned as prime minister last night, allowing David Cameron to take over.
Former foreign secretary Mr Miliband has never voted against gay rights and has only been absent for four gay-related votes.
Earlier this month, a poll of nearly 1,000 PinkNews.co.uk readers placed him as the most popular choice to take over from Gordon Brown.
Thirty-one per cent of our sample backed him for the Labour leadership, followed by 14 per cent for Mr Johnson and 11 per cent for Harriet Harman.
Mr Miliband is the only contender yet to declare his bid.
Ms Harman is currently deputy leader of the party and has been appointed caretaker leader in the interim. She was expected to run for the leadership but has ruled herself out of the contest.
Others expected to contest for the leadership are former schools secretary Ed Balls, former health secretary Andy Burnham and Mr Miliband’s brother Ed Miliband, who is seen as an outside contender.