The Prime Minister will table a motion to call for a general election on Monday amid a tense tussle over his Brexit deal.
Boris Johnson wrote to Labour leader Jeremy Corbyn this afternoon, and said he will give MPs more time to debate his Brexit deal if they agree to a December 12 general election.
It means he has abandoned he do or die pledge made in Wakefield in September that he would rather be "dead in a ditch" than delay Brexit past October 31.
He said: "I'm afraid it looks as though our EU friends are going to respond to Parliament's request by having an extension, which I really don't want at all.
"So, the way to get this done, the way to get Brexit done, is, I think, to be reasonable with Parliament and say if they genuinely want more time to study this excellent deal they can have it but they have to agree to a general election on December 12."
Labour will now have to decide how to respond.
There had been reports Labour was split over whether to back a general election, which would need a two thirds majority to go ahead in December.
His two previous attempt to call an election have been blocked because Labour has refused to support him.
Barry Sheerman, Labour MP for Huddersfield, said he would do the same again. He said: "I'm not voting for any election on Johnson's terms."
Hemsworth MP Jon Trickett, also Labour, tweeted: "Looks certain that Boris 'do or die by October 31' Johnson has broken his solemn vow. He must now face the electorate.
"But this election will be about more than Brexit. It's about building a new country."
While Rachael Maskell, Labour MP for York Central, added: "The Tories are pushing for a general election because they want a no deal option available. York with be the 8th worst hit place in the UK from no deal. Reckless."
Both Bradford West's Naz Shah and Rotherham's Sarah Champion said they would vote with Labour, when the party decided on its response.
But Mr Johnson warned Labour not to try to block an election.
"I think it would be absolutely morally incredible if they were to do so," he said.
"If Jeremy Corbyn and the Labour Party refuse to go along with this deal ... then you have to ask what is the purpose they think they would be serving in Parliament."
He added: "We would campaign day after day after day for the people of this country to be released from subjection to a Parliament that has outlived its usefulness.
"It is time frankly for this Parliament to make way for a new, fresh parliament that can deliver on the priorities of the British people."
It comes amid signs the EU is set to grant a fresh Brexit delay until the end of January after Mr Johnson was forced - under the terms of the so-called Benn Act - to request a further extension.
He has said that if that happened he would abandon his attempts to get his Brexit deal through Parliament and go for an election instead.
Earlier, shadow chancellor John McDonnell refused to be drawn on what they would do if he made a third attempt.
"We will see what happens. We are trying to take this in stages. We will confront that hurdle when we see it," he told reporters at Westminster.
With the EU expected to formally announce its decision on an extension of Friday, the Cabinet has met in political session to discuss its next move.
It could see ministers table a motion under the Fixed Term Parliament Act on Monday which could pave the way - if it is passed - for the first December election since 1923.
Earlier, Conservative Party chairman James Cleverly accused Labour of "running scared" of voters amid continuing "confusion" over its position on Brexit.
"We've been calling for a general election, me personally, the Prime Minister, my friends and colleagues all around the country, for months now," he told the BBC Radio 4 Today programme.
"The Labour Party are running scared and I can completely understand why, their Brexit message is confused at best."
His attack came amid reports of widespread opposition to an early election among Labour MPs, with the party trailing in the polls.
Mr McDonnell acknowledged there was "a difference of views" within the party but added: "Once an election is in the offing people usually rally together."