Jeremy Corbyn told MPs he can be the next Prime Minister, despite opinion polls pointing towards a mauling for Labour on June 8.
The Labour leader told MPs at a meeting of the parliamentary party in Westminster that he did not underestimate the challenge ahead, but welcomed the opportunity to offer voters a chance to elect an alternative government.
He faced calls from some MPs for Labour to abstain in the vote on Wednesday to approve the snap poll, in the hope of forcing Theresa May to call a vote of no confidence in her own government.
An aide later insisted Labour will vote to hold the election, but declined to say whether a three-line whip will be imposed.
Suggestions that Mr Corbyn would require MPs to face a "trigger ballot" of constituency members to secure their place as candidates were scotched, as a senior aide confirmed that all sitting MPs will be deemed to be automatically reselected.
The decision is expected to be rubber-stamped at a meeting of the party's ruling National Executive Committee on Wednesday, but the aide refused to say whether Mr Corbyn's wishes had been thwarted, saying only that there had been "a discussion" on the issue.
Meanwhile, a prominent backbench critic of the leader announced that he wanted to stand for re-election as a Labour MP but would not endorse Mr Corbyn for Prime Minister.
In a video message to voters in Barrow and Furness, John Woodcock said: "I am intending to seek renomination from my local Labour and Co-operative parties to be their official candidate, but I will not countenance ever voting to make Jeremy Corbyn Britain's Prime Minister."
Mr Woodcock said his opposition was founded in part on Mr Corbyn's opposition to the Trident nuclear deterrent, which is a crucial provider of jobs in the Cumbria constituency.
But he added: "I can't countenance endorsing him for a role which I think even he, though he may say differently in front of the cameras, does not think he is fit to carry out."
Mr Corbyn won brief but polite applause after addressing MPs at an evening meeting of the Parliamentary Labour Party, after arriving late due to being delayed on a train back from a visit to Birmingham.
Shadow chancellor John McDonnell said there was a "great atmosphere" in the packed meeting, while deputy leader Tom Watson described it as "very buoyant".
The Birmingham visit to promote Labour's plans to increase the carer's allowance was transformed into an impromptu election speech after Mrs May's surprise announcement.
The Labour leader said he wants to lead a government to "transform this country", ending austerity and tackling inequality.
But in order to do so he will have to defy opinion polls which have put his party a clear distance behind the Tories, and secure more seats than Ed Miliband managed in 2015.
And he will have to do that while at the helm of a party still deeply split in Westminster about his leadership, with some MPs preferring to quit rather than face an election.
The latest Press Association analysis of opinion polls put the Tories on 43 per cent, a 17-point lead over Labour's 26 per cent.
Given that Labour secured 99 fewer seats than the Tories in 2015, when the polls were much closer, the scale of the challenge facing Mr Corbyn is clear.
Asked if he was the next prime minister, Mr Corbyn said: "If we win the election, yes. And I want to lead a government that will transform this country, give real hope to everybody and above all bring about a principle of justice for everybody and economic opportunities for everybody."
Challenged on whether he would quit if the party failed to win, he said: "We are campaigning to win this election, that's the only question now."
In a sign of the discontent within the Labour ranks, Tom Blenkinsop immediately said he would not stand for re-election.
The MP criticised the leader last week after Labour lost a Middlesbrough council seat to the Tories on a by-election swing of 8%.
He said: "I have made no secret about my significant and irreconcilable differences with the current Labour leadership. It is because of these differences I feel I cannot in good faith stand as the Labour candidate for Middlesbrough South and East Cleveland."
Additional reporting by the Press Association.