Six candidates – Rebecca Long Bailey, Sir Keir Starmer, Emily Thornberry, Lisa Nandy, Jess Phillips and Clive Lewis – set out their stalls in Parliament on Tuesday evening.
Addressing the Parliamentary Labour Party (PLP), shadow business secretary Ms Long Bailey said that in losing the election, Labour “let down the people who rely on us”.
“Our number one duty as Labour MPs is to learn the lessons of defeat and make sure we don’t repeat them,” she told the private meeting.
How will the election campaign pan out over the coming months?
Earlier, the frontbencher insisted that she was not the “continuity candidate” to replace Mr Corbyn, but gave him a “10 out of 10 rating” – describing him as “one of the most honest, kind, principled politicians I’ve ever met”.
She told ITV News: "What we can’t ignore was that Jeremy was savaged from day one by the press … We have a role as party to develop the image of our leader and to put them forward in the most positive way, but we also have a duty to rebut criticism and attacks.
"As a party we needed to have a rebuttal unit, a clear structure in place to rebut the attacks against him.”
Shadow Brexit secretary Sir Keir told the hustings that the party needs to “win back our heartlands”.
He said: “We need to understand and to address each and every reason we lost at this election, but we also need to win back Scotland, we need to win back seats in Wales, and if you draw a line from London to Bristol and look south we only have a handful seats.
“So, we have got a mountain to climb.”
Rival Lisa Nandy, the MP for Wigan, said the leadership debate was “possibly the most important in our history”.
“Now is not the time to steady the ship. If we do not change course we will die and we will deserve to,” she added.
Jess Phillips told the hustings she does not want to be the next leader of the opposition, but rather “the next Labour prime minister – I want the people here to be in government”.
“I have dedicated my life to trying to change the lives of others, but I am sick of just shifting the dial, I want to smash it,” the Birmingham Yardley MP said.
Labour candidate proposes 'Ministry of Fabulosity'
In the race for the deputy post triggered by Tom Watson’s decision to quit, shadow sport minister Rosena Allin-Khan and Labour’s only MP in Scotland, Ian Murray, became the latest candidates to launch their bids.
She said: “It’s a real ministry, it will have to be dominated by fabulous MPs and come out with fabulous policies to shape the country.
“Some serious ones, but some lighter more entertaining ones about he we see ourselves and some of the things we can do as a nation to put a swing in our step.”
Asked what kind of policies, she said: “Political debate, there is room for traditional political debate, but sometimes there is room for a dance off. Sometimes you need to know how your political representatives can represent themselves in real life. We all love a boogie.”
The new Labour leader and deputy will be announced at a conference on April 4.