Video report by ITV News Political Correspondent Romilly Weeks
Theresa May will stand down as Prime Minister once her Brexit deal has passed, she has told Tory MPs.
In a meeting with the 1922 Committee in Westminster, Mrs May told Conservative MPs she had "heard very clearly the mood of the parliamentary party", adding "she would not remain in post for the next phase of the negotiations".
The Prime Minister did not name a date for her departure from 10 Downing Street, but her announcement sets the stage for a Conservative leadership election within the coming weeks or months.
But hours after Mrs May's announcement, the Democratic Unionist Party said it would not support the Government if it tables a fresh meaningful Brexit vote because "the necessary changes we seek to the backstop have not been secured".
In a statement the DUP said: "The backstop if operational has the potential to create an internal trade border within the United Kingdom and would cut us off from our main internal market, being Great Britain.
"We want to secure the United Kingdom's departure from, and our future relationship with, the European Union on terms that accord with our key objectives to ensure the integrity of the United Kingdom.
"In our view the current withdrawal agreement does not do so and the backstop, which we warned this Government against from its first inception, poses an unacceptable threat to the integrity of the United Kingdom and will inevitably limit the United Kingdom's ability to negotiate on the type of future relationship with the EU."
In a bid to get her deal passed by Parliament Mrs May acknowledged "the desire new leadership".
She told Tory MPs: "I know some people are worried that if you vote for the Withdrawal Agreement, I will take that as a mandate to rush on into phase two without the debate we need to have. I won't - I hear what you are saying.
"I am prepared to leave this job earlier than I intended in order to do what is right for our country and our party."
Her announcement comes as Parliament faces a crucial evening of votes that will determine how the Brexit process will play out.
In response to Mrs May's message, Tory MP Anna Soubry tweeted it was "shameful" that "Brexiteers will vote for the PMs 'deal' not because it's good for our country and the right thing to do ...but because it gets rid of the PM".
What are MPs voting on?
MPs voted on a series of Brexit plans to find out which one has the most support in Parliament after it seized control of the Commons agenda.
Speaker John Bercow chose eight motions MPs will vote on. These are:
No deal - moved by Tory MP John Baron.
Common market 2.0 - moved by Tory MP Nick Boles.
Efta and EEA - moved by Tory MP George Eustice.
Customs union - moved by Tory MP Ken Clarke.
Labour's alternative plan - moved by Labour leader Jeremy Corbyn.
Revocation to avoid no-deal - moved by SNP MP Joanna Cherry.
Confirmatory public vote - moved by Labour MP Dame Margaret Beckett.
Contingent preferential arrangements - moved by Tory MP Marcus Fysh.
But, MPs failed to back any of them. Ahead of the votes Bercow reinstated that Mrs May would not be allowed to bring her deal back for a third Meaningful Vote unless it had substantial changes.
His remarks came moments before Brexit Secretary Stephen Barclay revealed the Government would table a motion to enable the Commons to sit on Friday as it bids to secure approval for its deal.
Will Mrs May's decision sway MPs?
Boris Johnson has decided he will back the Prime Minister's deal but said nothing about his change of heart as he left the ERG meeting on Wednesday night.
Tory MPs Pauline Latham and Shailesh Vara told ITV News they will now switch and back the PM’s deal.
However, not all Tory MPs have been swayed by the Mrs May's announcement.
Conservative MP Anne Marie Morris told ITV News Political Correspondent Daniel Hewitt she would not vote the Prime Minister's deal based on her decision to stand down.
Reaction to Mrs May's decision
ITV News Political Editor Robert Peston said the Prime Minister's decision placed British politics in "new territory".
He said: "Never in our lifetimes has a Prime Minister promised to resign in order to get a policy through."
Leaving the meeting, European Research Group chairman Jacob Rees-Mogg said: "The Prime Minister was incredibly dignified. Although I was involved in the challenge against her last year, there is never any joy or happiness in somebody's political career coming to an end.
"There's always a poignancy about that and I think the Prime Minister did do it in an amazingly dignified way, and that is right and proper.
"Although I don't agree with her on everything, I have always greatly respected her approach to doing her duty and I think that shone through."
It was unclear whether the PM would regard herself as obliged to stand down if her deal was defeated or the Government held back from tabling it.In those circumstances, Mr Rees-Mogg said she "would have every right to carry on" as PM.
Conservative former minister Stephen Crabb tweeted: "Given the crap over the last few days PM spoke with remarkable dignity at 1922 mtg. Perhaps time now for ERG to consider disbanding. Time to get back to being one Conservative Party with one leader, one chief whip etc."
Labour MP David Lammy tweeted: "It is right that Theresa May goes, but this just raised the stakes even higher. The choice the country now faces is stark: a future relationship negotiated by a hard right PM chosen by Tory activists, or Remaining in the EU. The public must get to decide #PutItToThePeople."