Should this happen at the conclusion on Tuesday evening's vote, then it leaves the government just 17 days until the Brexit deadline and no room left to negotiate as the EU has already said that they will not spend any more time debating with the government.
So, what does all of this mean? With many scenarios still at risk and Theresa May's premiership looking more and more uncertain these are potentially the 4 key moments which could affect the future of Brexit and the prime minister.
1. May's deal is narrowly defeated
As with some previous votes, although May has lost she has only done so by a handful of votes. Should this happen again then she would be theoretically safe, for now but on thin ice.
On the other hand, this would leave Brexit in a right old state and wherever it goes next is virtually unknown territory.
2. The deal gets heavily defeated igniting a vote on no-deal
In the likely scenario that the deal is defeated by a considerable margin, the Brexit situation will look more and more precarious for the government.
This would then set in motion a series of events which could severely impact Theresa May's position after she had promised to allow MPs to vote on a no-deal.
A non-binding agreement was previously voted on by the Commons which indicated that parliament would reject a no-deal but would still stand if there was nothing was agreed by March 29.
As you can imagine this would be a highly embarrassing situation for the PM, leaving her on very thin ice.
3. Article 50 gets extended
Along with a no-deal vote a vote on Article 50 being extended, which would only happen if a no-deal is rejected.
Labour has suggested that they would whip their MPs to support an extension which needs to be supported by the British government before it can be approved by the EU.
Should Article 50 get extended, the government can go back to the EU and negotiate a new deal which could come in the form of the so-called 'Norway model.'
4. General election or vote of no confidence
This is where things could get a bit dicey for May where she could call for another snap general election to secure a more concrete mandate on her deal.
There is always the chance that the Tories could lose that election handing power to Labour and gifting them the ability to negotiate Brexit on their terms.
However, Labour could call for another vote of no confidence against May, which she of course survived last time but is not certain to win again in these otherwise uncertain times.
Should May lose a vote of no confidence it would trigger a general election anyway, so that might be the best solution for Labour at this time.
This could, of course, untie the Conservatives as it did previously but given that she would have already faced two no-confidence votes in such a short amount of time, then she may hang up boots and decide to resign.