Jess Phillips has quit the race to replace Jeremy Corbyn as Labour leader.
The Birmingham Yardley MP made it through to the second round of the leadership race but has decided to withdraw, stating she is not the candidate to "unite all parts of our movement".
In a message to supporters, she said: "The Labour Party needs to elect a candidate who can bring all parts of our movement together. And at this time, if I am honest, that candidate is not me."
She leaves behind Sir Keir Starmer, Rebecca Long-Bailey, Lisa Nandy and Emily Thornberry vying for the position.
Ms Phillips, 38, also said she hope to do "everything within my power" to help facilitate the election of a unifying leader.
"To win again, to do all of the things that we need a Labour government to do, we must elect a leader who can bring us together, end the division and rebuild trust with the country," she said.
"I will do everything within my power to ensure that’s the case."
A longstanding critic of Jeremy Corbyn, she described Labour's defeat at the last election as "cataclysmic".
"I'm now going to go out into the country and join the fightback," she said in a video message to supporters. "Because the Labour party is not about what job description you have. We are the strength of our common endeavour.
"We go out into the country, in the local elections, the mayoral elections and we fight back. And we make sure that we are out there, speaking to the country, and making sure that the Labour party can win elections again."
Ms Thornberry, who Ms Phillips had been running against, said she was "very sorry" to see her drop out.
"We need to broaden our debate, not narrow it, and force the two favourites to prove they're up to the fight by pitting them against some real strength," she tweeted.
"Jess is a sad loss in that effort, but we will keep going."
Ms Nandy, who remains in the contest, tweeted: "I'm sorry to see Jess drop out. She has made waves, shown great friendship and I’ll miss her in this contest."
Earlier on Tuesday, Ms Phillips missing from a hustings event organised by the GMB union - whose support could prove crucial to the candidates still hoping to make it on to the final ballot paper.
I'm very sorry to see @jessphillips drop out of the contest - we need to broaden our debate, not narrow it, and force the two favourites to prove they're up to the fight by pitting them against some real strength. Jess is a sad loss in that effort, but we will keep going.— Emily Thornberry (@EmilyThornberry)January 21, 2020
I'm sorry to see Jess drop out. She has made waves, shown great friendship and I’ll miss her in this contest.— Lisa Nandy (@lisanandy)January 21, 2020
Aides had said her absence from was due to an unavoidable appointment elsewhere, ahead of her making the statement on Tuesday afternoon.
Previously she said it would be a "bold roll of the dice" for Labour members to elect her as leader.
Candidates need the nominations of three Labour affiliates, including at least two unions, amounting to at least five per cent of affiliate members to make it to the final ballot paper.
Sir Keir has been touted as the frontrunner in the race having achieved this already.
The ballot for the leadership opens on February 21 and closes on April 2.
The results will be announced on April 4.