Theresa May will be forced to come back to the House of Commons within three sitting days with fresh proposals if her Brexit deal is defeated next week.
An amendment tabled by Tory MP Dominic Grieve passed this afternoon by 308 votes to 297.
The result forces the Prime Minister to come back within three sitting days with proposals for next steps if the Chequers deal fails to win a majority of support.
The vote is a significant shift of power back in favour of the Parliament.
It comes less than 24 hours after Mrs May suffered a major backbench rebellion with MPs signalling their opposition to a no-deal Brexit by defeating the Government in the House of Commons last night.
Jeremy Corbyn had earlier demanded Mrs May called a general election if her Brexit deal wass defeated next week.
The Labour leader also repeatedly pushed Mrs May to rule out a no-deal Brexit as Europe dominated their exchanges at Prime Minister’s Questions today.
The PM defended her Government’s efforts to prepare for the prospect of the UK leaving the EU without a deal and dismissed holding a general election.
She also attempted to ease concerns over Northern Ireland by insisting the Commons will get a vote on whether to extend the Brexit transition period or trigger the backstop if no trade deal is concluded by the end of 2020.
Mr Corbyn described this proposal as “window dressing”. He said MPs wanted to see “clear legal changes” to the Withdrawal Agreement.
He went on to accuse Mrs May of “recklessly wasting time” and “holding the country to ransom with the threat of a no deal”.
Mrs May gave a nod to the pre-Christmas row, which saw Mr Corbyn accused of muttering “stupid woman”, a claim he denied, as she replied: “The only way to avoid no deal is to vote for the deal. If he is uncertain about what I am saying perhaps I can give him a tip – he might like to use a lip reader.”
The Opposition leader pressed further on getting guarantees from Mrs May about legal changes to the Brexit deal before listing concerns over no-deal raised by Cabinet ministers.
He said: “The £4.2 billion of public money is being wastefully allocated to no-deal planning.
“Will the Prime Minister listen to the clearly expressed will of the House last night, end this costly charade and rule out no deal?”
Mrs May reiterated a deal must be backed to avoid a no-deal Brexit, noting: “He stands there complaining about money being spent on no-deal preparations.
“So, on Wednesday he’s saying we shouldn’t be spending money on no-deal preparations. On Monday he said no-deal preparations were too little too late.
“He can’t have it both ways – either we’re doing too much or too little.
“So perhaps he can break his usual habit and actually give us a decision - which is it?”
Mr Corbyn again pushed for no-deal to be ruled out before telling the Commons: “The Prime Minister has spent the last week begging for warm words from EU leaders and achieved nothing, not one single dot or comma has changed.
“She’s already squandered millions of pounds of public money on last-minute, half-baked planning for a no-deal that was rejected last night.
“So, if her deal is defeated next week, as I hope and expect it will, will the Prime Minister do the right thing and let the people have a real say and call a general election?”
Mrs May replied: “No. We’ve put a good deal on the table that protects jobs and security.
“But I noticed in all of that we still don’t know what Brexit plan [Mr Corbyn] has.”
Mrs May highlighted apparent contradictions in Mr Corbyn’s approach to Brexit, adding: “The one thing we know about [Mr Corbyn] is his Brexit policies are the many, not the few.”
Both leaders began PMQs by condemning abuse hurled at MPs and journalists in the areas surrounding Parliament.
It comes after Conservative former minister Anna Soubry was branded a “Nazi” by protesters during television interviews.
The PM said: “Politicians and the media should be able to go about their work without harassment and intimidation.”
Mr Corbyn added: “We have to be clear that intimidation is wrong outside this building, as it is wrong in any other aspect of life in this country, and we have to create a safe space for political debate.”
SNP Commons leader Pete Wishart later described the Prime Minister’s deal as the “deadest dodo”.
He said: “Parliamentary defeats are now a regular feature of her Government. She’s lost a quarter of her Cabinet and 117 of her backbenchers want her gone. Her deal is as dead as the deadest dodo.
“How many more indignities can this Prime Minister endure before she realises that she is the biggest part of this problem and for goodness’ sake just go?”
Mrs May responded, saying her Government had negotiated a deal that “delivers on the referendum result”.
Labour MP Stephen Kinnock (Aberavon) pushed Mrs May to give MPs, including Government ministers, a free vote to decide the next course of action if her deal is rejected on Tuesday.
She replied: “I am working to ensure that the deal that has been negotiated by the UK Government with the European Union is voted positively on by this Parliament.”