Liz Kendall has become the first Labour MP to declare that she will seek the party leadership after Ed Miliband's resignation.
The shadow health minister announced her intention to vie for the party leadership while speaking on BBC1's Sunday Politics today.
She has already been touted as one of the favourites along with the likes of Chuka Umunna, Yvette Cooper and Andy Burnham.
Asked if she was standing on the BBC show, Ms Kendall gave a firm "yes", though she admitted it would be "phenomenally difficult" to sufficiently rebuild the party in time to defeat the Conservatives in 2020.
The Leicester West MP, 43, who entered the Commons in 2010, joined calls by ex-PM Tony Blair for the party to offer a more "aspirational" message that appealed beyond the traditional working class vote.
It was no good being a government that thought the answer was "doing things to people or for them", she said, and instead needed to ensure everyone had the opportunity to succeed for themselves.
"It is not just enough to critique what is going on; you have to set out something people can believe in", she said.
Potential rival Chuka Umunna declined to confirm that he would join the race to succeed Ed Miliband, who resigned after leading the party to a shocking defeat at the polls, when pressed on BBC1's Andrew Marr Show.
Mr Umunna rejected claims the scale of the defeat meant it could not return to power in 2020.
"We are down but we are not out," he told the programme.
"I do not buy this idea that this is somehow a 10-year rebuilding project."
Meanwhile, shadow education secretary Tristram Hunt said he is "definitely thinking about" running for Labour leader.
He also warned Labour is "in a hole" in Scotland and England and needed to appeal to traditional Labour communities plus the aspirational "John Lewis couple".
Tottenham MP David Lammy yesterday hinted he may join the race, saying he has been thinking "very, very carefully" at who can best take the party forward.
Additional reporting PA.
