Normanton, Pontefract and Castleford MP Yvette Cooper has said she will not stand for Labour leader.
The MP, who last month secured her seat with a majority of just 1,276 votes, made the announcement on Twitter this afternoon.
Ms Cooper, who came third in the party's 2015 leadership contest, had previously said she would decide over Christmas whether or not to stand for leader when Jeremy Corbyn steps down.
Writing on Twitter earlier today, she said she had decided not to stand, but would "keep fighting for a Labour Government".
She said: "The scale of Labour’s defeat challenges our whole party not just the next leader. I’m not standing for Labour leader this time but I’ll keep fighting for a Labour Govt.
"Our next leader will need support to rebuild."
Speaking at the general election last month, Ms Cooper said: "I want to thank particularly the people in Normanton, Pontefract, Castleford and Knottingley who voted for me today.
"But we have lost very many votes and we lost Labour votes right across the country and we have to be humble about that and we have to change.
"Of course this election has had Brexit as a key component and of course many things might have been different if we had reached some form of customs compromise in the spring or if maybe people had been able to work together in a way that didn't happen.
"But instead the polarisation across this country still feels very deep and very damaging."
Writing in the Guardian, she said that the new leader would need to stop factional infighting in the party and bring kindness and integrity back into politics.