UK and EU officials have agreed on the draft text of a Brexit agreement in a significant breakthrough for the talks.
A cabinet source told the BBC that the document has been agreed at a technical level by officials from both sides after intensive talks this week.
A special cabinet meeting will be held early tomorrow morning NZT as Theresa May seeks ministers' backing.
Every minister is being asked to see the prime minister for one-to-one talks before tomorrow's meeting.
The future of the border between Northern Ireland and the Republic of Ireland has been the last major outstanding issue to be settled amid disagreements over how to guarantee that there will not be physical checks reintroduced after Brexit.
Cabinet ministers have already been briefed on the state of the negotiations when they were told a "small number of outstanding issues" remained to be sorted.
Mrs May's officials said ministers were now being called to a special meeting to "consider the draft agreement the negotiating teams have reached in Brussels, and to decide on next steps".
Before they do so, they will be able to read relevant "documentation".
In another development, ambassadors from the remaining 27 EU states will meet in Brussels on Wednesday local time.
The prime minister has been under pressure from both Brexiteers and pro-EU MPs as she tries to seal a deal with the EU on the terms for the UK's exit on 29 March 2019.
Both the UK and EU want to schedule a special summit of European leaders at the end of November to sign off the withdrawal deal and an outline declaration of their future relationship.
The EU has insisted it would only agree to put the wheels in motion for the summit if agreement can be reached on the issue of the Irish border.
If a deal is agreed with the EU, Mrs May then needs to persuade her party, and the rest of Parliament, to support it in a key Commons vote.
Meanwhile, following pressure from all sides of the House of Commons, ministers have agreed to provide MPs with a legal assessment of the implications for the UK of the backstop and other controversial aspects of any deal.
The Democratic Unionists, on whom the PM relies for her Commons majority, said they would vote for Labour's motion urging disclosure of "the full and final advice" given by Attorney General Geoffrey Cox to the cabinet.
An influential group of Tory Brexiteers also said they would not oppose the move, which was later passed unopposed in the Commons.
Cabinet Office minister David Lidington said Mr Cox, who is the government's senior legal adviser, would make a statement to MPs and take questions ahead of the final vote on any Brexit deal.
MPs, he said, would get to see "a full reasoned position statement laying out the government's both political and also legal position on the proposed withdrawal agreement".
The concession reflects the wording of a compromise amendment supported by a number of Tory members of the European Research Group which was not selected for debate.
The DUP's Westminster leader Nigel Dodds said he was pleased Parliament had "asserted its will" as it was imperative that all parties to the deal were clear in what way and for how long it would "legally bind" the UK.
In a speech on Monday evening, Mrs May said the "endgame" in the negotiations had been reached and while both sides wanted an agreement, the issues at stake were "immensely difficult".
But Boris Johnson, who quit as foreign secretary in July in protest at Theresa May's strategy, hit out at what he claimed was a "stage-managed delay" in reaching an agreement.