MPs have rejected crashing out of the European Union without a deal, just 16 days ahead of the scheduled break from Brussels.
Events over the next 24 hours will have a major impact on how, when - and if - the UK leaves the EU.
What is happening in Westminster?
MPs will vote on whether Parliament wants to seek an extension to Article 50 - delaying the UK's departure beyond the current March 29 deadline - on Thursday.
Mrs May has stressed that would not resolve the divisions in the Commons and could instead hand Brussels the power to set conditions on the kind of Brexit on offer "or even moving to a second referendum".
The motion will be amendable, meaning MPs may try to gain a majority for the length of the delay or type of Brexit as part of the extension.
Meanwhile, the Commons Brexit Committee called on Wednesday for Article 50 to be extended, with "indicative votes" for MPs to signal their preferred way forward.
How could Brexit be delayed and for how long?
To secure an extension to Article 50, Mrs May would need the support of the 27 other EU states. They are likely to agree to an extension as long as there was a prospect of a deal being reached - or a referendum or general election which could change the political landscape at Westminster.
READ MORE: No-deal Brexit off the table as MPs reject leaving EU without a deal
European Commission president Jean-Claude Juncker said that Brexit should be completed before the European elections which take place between May 23 and 26.
"If the UK has not left the EU by then, it will be legally required to hold these elections," he said.
If a longer extension was sought, that would mean taking part in the elections, something likely to fuel Eurosceptic anger - and potentially see Nigel Farage standing for the new Brexit Party.
What have the EU 27 leaders said?
Ahead of the no-deal vote, German Chancellor Angela Merkel refused to say how long she thinks a possible delay to Brexit should be, but said it was in "our mutual interest that we achieve an orderly departure".
French president Emmanuel Macron said Britain needed a clear reason for requesting an extension and extra time could not be used to renegotiate the withdrawal.
The EU's chief Brexit negotiator Michel Barnier said London must decide what it wants from Brexit before Brussels will consider a delay.
Will the Prime Minister seek further changes in Brussels?
Mr Juncker was clear during his meeting with the Prime Minister in Strasbourg that there was no more room for movement.
"In politics, sometimes you get a second chance. It is what we do with this second chance that counts. Because there will be no third chance," he said.
"There will be no further interpretations of the interpretations; and no further assurances of the re-assurances."
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But a European Council summit on March 21 could give Mrs May one last chance to persuade her fellow leaders face-to-face that she needs extra help to get a deal over the line.
So what happens on March 29?
It is still impossible to say. If a deal is somehow reached and legislated for then, although the UK will formally leave the EU at 11pm, very little will change as a transition period will smooth progress to the UK's new future.
If there is a delay, the UK will still be in the European Union until the extension period expires.
But if there is a no-deal Brexit, things are a lot more uncertain - the Government has been ramping up preparations to try to prevent shortages of food and medicine amid fears that increased bureaucracy will clog up key ports where goods arrive from the Continent.
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