Dan Jarvis has ruled out himself out of the Labour leadership contest, one of the early favourites to succeed Ed Miliband insisting he wanted to put his children before his immediate political career.
The ex-Army paratrooper, who gave up his military career to become an MP in 2011, had been seen by many in the party as an ideal candidate to give the party a fresh start.
But Jarvis, who held his Barnsley Central seat with an increased majority, said while he wanted to be part of the "rebuilding process" he could not take the top job.
He said the general election "delivered a devastating result for the Labour Party and the prospect of five bleak years ahead for our country".
"I'm ready to serve in that rebuilding process as part of the Labour team. But I can't do that as leader at this moment and I won't be putting my name forward in the coming leadership contest," he said.
"My eldest kids had a very tough time when they lost their mum and I don't want them to lose their dad. I need some space for them, my wife and our youngest child right now, and I wouldn't have it as leader."
Joining a wave of stinging internal criticism of Miliband's campaign, he said Labour had allowed the Tories to appear "more serious than us about spreading wealth across the country.
"Never again can we allow ourselves to be painted as having a problem with people eager to work hard, get on and succeed. They should know that Labour will always be their champion."
Jarvis recently remarried after losing his first wife after a four-year battle against cancer in 2010.
His announcement leaves shadow health minister Liz Kendall the only declared candidate - with shadow business secretary Chuka Umunna and shadow education secertary Tristram Hunt dropping hints they would also join the race.
Umunna earlier said he would "play the fullest part I can" while Hunt said he is "definitely thinking about" running for Labour leader.
Mr Jarvis said the nature of Labour's defeat meant the party must "fundamentally question our future direction" and "take our time to reflect, renew and reconnect".
"It was a judgment on our failure to move out of the comfort zone of critiquing the Tories and instead set out a positive alternative. The Labour Party has no divine right to expect the support of the British people. We have to earn it."
Echoing demands for a more "aspirational" approach from a stream of critics of a leftwards shift under Miliband, he said the party "failed to tap into people's aspirations with a sufficiently optimistic vision for how Labour would improve their lives".
He said there had to be more honesty about the failings of economic policy of the last Labour government and action to revive local parties that had "stagnated and failed to reach out to their communities".
Fellow MPs applauded his decision but regretted the loss to the potential line-up - which it is thought could eventually also include shadow health secretary Andy Burnham and shadow home secretary Yvette Cooper.
"Not just another me, me, me MP. Precisely why he would have been good. Impossible not to respect his values," John Mann wrote on Twitter.
Jamie Reed said: "Bloody Dan Jarvis. Here's a man with an incredibly high stock, who, through basic decency, has sent it even higher."
The Parliamentary Labour Party will start to regroup at a Westminster meeting tomorrow under the interim leadership of Harriet Harman - who has said she will step down as deputy leader once a new leader and deputy has been elected.
In his statement, Jarvis did not explicitly rule out standing for the number two role.
A meeting of the National Executive Council is due in the coming days to thrash out a timetable for the election, with parts of the party already at odds over whether to have a short or longer contest.