Jeremy Corbyn has insisted he is "campaigning to win" despite Labour languishing in the opinion polls.
The opposition leader said he wanted to be the next prime minister and head a government that would "transform this country".
He was speaking after Theresa May's shock announcement that she would move to hold a national poll on 8 June.
However, Mr Corbyn goes into the planned election at the head of a divided party, with Labour finishing 21 points behind the Conservatives in a recent YouGov poll about voting intentions.
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."
However, in a sign of the splits dogging Labour, backbencher Tom Blenkinsop immediately said he would not seek re-election.
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."
Meanwhile, David Cameron has hailed Theresa May's "brave" decision to call a snap election.
The former premier, who quit Downing Street following last year's Brexit vote, tweeted: "Brave - and right - decision by PM @Theresa_May. My very best wishes to all Conservative candidates."
SNP leader Nicola Sturgeon branded the announcement as "one of the most extraordinary u-turns in recent political history" and argued Mrs May was "once again putting the interests of her party ahead of those of the country".
Scotland's First Minister said: "She is clearly betting that the Tories can win a bigger majority in England given the utter disarray in the Labour Party.
"That makes it all the more important that Scotland is protected from a Tory Party which now sees the chance of grabbing control of government for many years to come and moving the UK further to the right - forcing through a hard Brexit and imposing deeper cuts in the process."
In a message to voters, Liberal Democrat leader Tim Farron said: "This is your chance to change the direction of your country.
"If you want to avoid a disastrous hard Brexit. If you want to keep Britain in the single market. If you want a Britain that is open, tolerant and united, this is your chance.
"Only the Liberal Democrats can prevent a Conservative majority."
UKIP leader Paul Nuttall said: "We are in the midst of Brexit negotiations so this election will provide a perfect opportunity for the 52% to vote for UKIP, the only party wholeheartedly committed to a clean quick and efficient Brexit."