The Commons Speaker John Bercow has given the green light to a debate as Tory rebels seek to gain control of the House of Commons agenda.
He also granted a vote on taking control of the Commons agenda.
If successful, it would allow the MPs to bring forward a bill seeking to delay the proposed Brexit date beyond October 31.
Officials for No 10 have warned that the Prime Minister Boris Johnson will drive for an election if the vote is successful.
The debate can last got up to three hours and the main vote is expected at around 10pm.
If the vote is successful, it means the MPs will be able to take control of Commons business on Wednesday.
It will give them the chance to introduce a new bill that would force Boris Johnson to ask for a Brexit delay until January 31 2020.
It would be in place unless a new deal is approved by MPs or in the eventuality they vote in favour of no-deal.
The emergency debate was initially proposed by Tory rebel Sir Oliver Letwin.
He accused the MP of having "no credible negotiating strategy" and said a no-deal scenario was a "threat" to the UK.
The move was backed by the Labour leader Jeremy Corbyn, who described it as the "last opportunity" to block no-deal.
"If we don't take action today, we may not get another chance," he said.
The Commons leader Jacob Rees-Mogg criticised the Speaker's decision to allow the vote on the Commons agenda.
Mr Rees-Mogg described those supporting the emergency motion as an "Illuminati who are taking the powers to themselves".
He added: "It is not, however, for Parliament to undertake the role and functions of the executive.
"Constitutional convention is that executive power is exercised by Her Majesty's Government which has the democratic mandate to govern.
"That mandate is derived from the British people and represented through this House.
"When we look at this constitution we are protected by our rules and our orders and by our conventions."
The Commons Leader: "It is those rules, those laws, those conventions that protect us from the winds of tyranny."
He added that the Lewtin motion is "the most unconstitutional use of this house since the days of Charles Stewart Parnell when he tried to bung up Parliament."