MPs are expected to meet in the Commons on Saturday October 19 - the deadline by which Boris Johnson has to either agree a Brexit deal or ask for an extension to Article 50.
It will be only the fifth time the Commons has met on a Saturday since World War II.
The emergency sitting is set to coincide with a mass pro-second referendum march in central-London.
The government is expected to ask MPs to sit regardless of whether the prime minister has secured an agreement on an exit deal at next week’s crucial EU summit.
The EU Council meeting in Brussels on October 17 and 18 is the last scheduled meeting of EU leaders before Britain is supposed to leave on October 31.
If the PM wins agreement for a deal at the last minute, MPs will be asked to vote for it on Saturday. If not, they can be expected to debate what next steps to take.
Johnson has pledged to take the UK out of the EU by the end of this month with or without a deal.
But the so-called Benn Act passed by MPs opposed to a no-deal exit requires Johnson to ask for a delay if no agreement has been reached by October 19.
Ministers have insisted Johnson will comply with the law, but Westminster has been gripped with speculation that No.10 will somehow try and bypass the legislation to avoid an extension.
MPs have met on a Saturday only four times since 1939. The Commons sat on Saturday, September 2 at the outbreak of World War II. It met for the last sitting of the summer on September 2, 1949. MPs debated the Suez Crisis on November 3, 1956. And the Commons returned on Saturday, April 3, 1982 for the Falkland Islands invasion.
Johnson may have cobbled together a proposal that could win a majority in the Commons amid signs that some Labour MPs would be prepared to vote for it.
Caroline Flint is one of 19 Labour MPs to have signed a letter asking the UK and EU to “work night and day” to reach an agreement and that it would be in the “national interest” for the Commons to approve it.
She told BBC Radio 4’s Today programme this morning that “stopping no-deal has to be done with a deal”.
But the prime minister’s chances of a breakthrough with Brussels were looking increasingly unlikely after accusations from No.10 that the bloc was making it “essentially impossible” for Britain to leave with a deal.
Johnson will hope to gain concessions from his Irish counterpart Leo Varadkar during in-person talks anticipated later this week. But Varadkar told RTE it was “very difficult” two sides to reach an agreement before the October 31 deadline.