A majority of MPs are expected to demand that a "no deal" Brexit be taken off the table, although it is unclear how that could be imposed on the government.
Responding to the defeat, May said: "The House has spoken and the Government will listen". As you said I think it's unlikely to succeed but we have got to see if a general election could resolve the issue. "Nothing about how - or even if - it intends to honour the decision the British people took in a referendum Parliament chose to hold".
EU Council chief Donald Tusk tweeted seconds after the vote: "If a deal is impossible, and no one wants no deal, then who will finally have the courage to say what the only positive solution is?"
Pro-Brexit Conservatives, who tried and failed to unseat May as Prime Minister in a confidence vote last month, believe Downing Street is playing up reports that the margin of defeat for May's bill could be higher than 200 - making it the worst for a Prime Minister in British history - as a way of managing expectations and making a narrower defeat look like a minor victory.
'We are calling for an extension to the transition period in order for Parliament to decide what our next steps are; whether that is a new deal, a referendum, an orderly exit from the European Union without a deal at a later date, or a general election.
"Enough time has been wasted".More news: Kanye Compares R. Kelly To Michael Jackson - Kim Kardashian Tries To Explain
The vote will decide whether the Parliament is willing to back the controversial deal Prime Minister May had such a hard time negotiating with Brussels.
He said: "This deal is better than staying in they European Union - we will be out of the Common Fisheries Policy, out of the Common Agricultural Policy, out of the relentless momentum for political integration".
Theresa May's government will face a vote of no confidence today that it is bound to win since none of her own MPs nor the Democratic Unionist Party is prepared...
Tuesday night's vote was the product of more than two and a half years of tortuous debate and negotiations, after 51.9% of British people voted to leave the European Union in 2016.
"Theresa May has somehow achieved the unachievable by uniting the majority of the country in that people from both sides - remain and leave - both want her deal to be voted down".
The proposal was roundly rejected by both supporters and opponents of Brexit.
The EU's chief negotiator Michel Barnier said last night: "Now it is time for the United Kingdom to tell us the next steps".More news: City can't afford £100m Ruben Neves, says Pep Guardiola
Attorney General Geoffrey Cox told lawmakers in the House of Commons it would be "height of irresponsibility" to reject the agreement and plunge the country into uncertainty.
"We'll have further preparations at cabinet tomorrow for no-deal Brexit". One amendment from the Labour Party rejects May's deal and also rules out leaving the bloc without agreement, while one from the Scottish National Party seeks to postpone Britain's departure from the EU.
"While no deal remains a serious risk...it is now my judgment that the more likely outcome is a paralysis in Parliament that risks there being no Brexit", said May.
Former minister Nick Boles, meanwhile, set out a plan by which senior MPs would take control of the Brexit process if the government couldn't get anything through Parliament.
Check back on inews.co.uk for a live stream of the vote as it happens in Parliament. Our conviction is based on the fact that it would require Conservative MPs to bring down the government, which we see little appetite for.
Optimism rose among anti-Brexit campaigners that they could overturn the "Leave" vote from the 2016 referendum, with many pinning their hopes on a new so-called people's vote to end the parliamentary deadlock.More news: U.S. girl, 13, found alive three months after murder of parents