Johnson returned from an EU summit in Brussels overnight for a busy day of meetings and phone calls as he attempted to persuade lawmakers to ratify the divorce deal at a rare Saturday sitting of Parliament.

He was to brief his Cabinet on Friday afternoon, ahead of what's expected

Johnson's Conservative Party holds only 288 seats in the 650-seat House of Commons, so he will have to rely on support from other parties and independent lawmakers to get over the line.

Foreign Secretary Dominic Raab started drumming up support early.

"We've got a real opportunity now to get Brexit delivered faithful to the referendum, move on as a government, and I think as a country, and lift the clouds of Brexit," he told the BBC.

Raab said the government has not given up hope of winning the support of its Northern Ireland ally, the Democratic Unionist Party, which has rejected the new deal.

But the chances of that appeared slim. The DUP's Brexit spokesman, Sammy Wilson, said Johnson's Brexit package - which carves out special status for Northern Ireland to keep an open border with EU member Ireland - is bad for his region and its bonds with the rest of the U.K.

"I can give you absolute assurance we will not be voting for this deal when it comes before the Commons tomorrow," he told the BBC.

The deal's fate could largely rest on a group of 21 Conservative lawmakers expelled from the party's group in Parliament earlier this year for voting against the government, and on members from the main opposition Labour Party, which has 244 lawmakers.

Nicholas Soames, one of the 21, said he would vote for the deal, and thought most of his expelled colleagues would "by and large vote for it."

Labour leaders have told party lawmakers to oppose the deal. But around 20 of them, mainly representing pro-Brexit parts of the country, have previously indicated a desire to back a deal to honor the June 2016 Brexit referendum result.

Labour lawmaker John Mann said Friday that he thought at last 10 party legislators would support the government's deal.

While a majority of members of Parliament supports leaving the EU, in keeping with voters' decision in a referendum more than three years ago, they are split on the terms. Labour lawmakers worry that the Johnson deal's vision of a loose post-Brexit economic relationship with the EU could endanger workplace and environmental protections that Britain gained as a member of the bloc.

Many legislators also want to rule out the possibility of crashing out of the bloc without a deal - a prospect economists say would disrupt trade and plunge the economy into recession.

While Saturday's vote will mark a defining moment, the Brexit saga may have more twists in store. Several lawmakers are trying to disrupt the vote with amendments that radically change it; one even calls for Britain to cancel Brexit altogether.

That has little chance of succeeding, but lawmakers could back another proposal, which would withhold approval of the deal until all the necessary legislation to implement it has been passed. It's intended to prevent any chance of a no-deal exit on Oct. 31, and could get support from lawmakers who want to leave the EU but fear the consequences of a chaotic exit.

It's a complex situation and not even expert analysts can gauge the exact numbers.

"There seems to be an indication that it will be very, very close, it will come down to one, two or five people," said Joelle Grogan, a senior lecturer in U.K. and EU law at Middlesex University. "But speaking only with 24 hours away, I have no idea what that will look like."

If Johnson's charm offensive manages to corral enough votes to pass the deal, Britain would be on course to leave the EU in an orderly fashion on Oct. 31 - although Parliament would still need to pass legislation to implement the decision.

If lawmakers reject the deal - as they did three times with an earlier agreement presented by Johnson's predecessor, Theresa May - a law passed earlier this year compels the prime minister to ask the EU for a three-month delay to Britain's exit date.

Johnson has said he won't do that, but also that he will obey the law, an apparent contradiction.

One Conservative lawmaker who repeatedly rejected May's deal and quit her government over that version, finally got on board Johnson's Brexit.

Suella Braverman tweeted that, "Tomorrow I will vote to support the new deal" that Johnson negotiated.

Asked Thursday what he would do if Britain seeks an extension, European Council President Donald Tusk said he would consult the other 27 EU nations to reach a decision.

European leaders are reluctant to prolong the Brexit melodrama further and have urged British lawmakers to back the deal and get it over with.

"I want us to finish this off and speak about the future," French President Emmanuel Macron said Friday at an EU summit in Brussels. "The Oct. 31 date must be respected. I don't believe new delays should be granted."