A Brexit deal has been agreed between UK and EU negotiating teams before a meeting of European leaders in Brussels.
Prime Minister Boris Johnson tweeted: "We've got a great new deal that takes back control."
The two sides have been working on the legal text of a deal, but it will still need the approval of both the UK and European parliaments.
The DUP has said it will not vote for the deal, potentially scuppering it.
In a statement, the Northern Irish party, which the government relies on for support in key votes, said: "These proposals are not, in our view, beneficial to the economic well-being of Northern Ireland and they undermine the integrity of the Union."
They added: "Saturday's vote in Parliament on the proposals will only be the start of a long process to get any Withdrawal Agreement Bill through the House of Commons."
Labour leader Jeremy Corbyn said the deal sounded "even worse" than what was negotiated by the PM's predecessor, Theresa May, and "should be rejected" by MPs.
But European Commission President Jean-Claude Juncker said it was a "fair and balanced agreement".
Both he and Mr Johnson have urged their respective parliaments to back the deal.
No 10 sources have told the BBC's political editor Laura Kuenssberg that Mr Johnson will later ask EU leaders to reject requests for an extension to the Brexit deadline of 31 October.
MPs passed a law in September that requires the PM to request an extension on 19 October if Parliament has not agreed a deal or backed leaving without a deal by that date.
MPs are voting on whether to hold an extra sitting in the Commons on Saturday to discuss the next steps.
Cabinet Office minister Michael Gove said if the sitting was approved, the government would hold a vote on the deal.
He said he was "not contemplating defeat", but if the plan did not get the backing of MPs, the alternative was leaving without a deal.
The DUP has been in an agreement with the Conservative Party since the 2017 election, which, in the past, gave the government a working majority.
But after resignations and the removal of the party whip from more than 20 Tory MPs in recent weeks, Mr Johnson now could face a tough battle to get his deal through Parliament.
Mr Barnier said he and Mr Juncker had been told by the PM "he has faith in his ability to convince the majority he needs in the House of Commons".
While Boris Johnson may have a deal in Brussels, he absolutely does not have a deal in Westminster.
The DUP isn't prepared to back this package because it does not give it a veto over the new customs arrangement, which it fears could threaten Northern Ireland's position in the United Kingdom.
Team Johnson hopes that, by presenting this as a choice between Mr Johnson's deal and no-deal, the DUP will buckle.
But the DUP doesn't blink easily, and if it doesn't, the signs are Mr Johnson could be defeated on Saturday, when the party's 10 votes could be critical.
That could trigger the Benn Act, forcing a lengthy delay, and could encourage some opposition MP to trigger a motion of no confidence, paving the way for a general election.
It's going to be a titanic tussle on Saturday.
Most of the deal is the same as the one agreed by Theresa May last year - the main change is the Northern Ireland proposals.
The DUP's objections
In a statement, the Democratic Unionists said Northern Ireland's main East-West trade route would still be subject to EU customs rules, "notwithstanding that Northern Ireland will remain part of the UK customs territory".
"All goods would be subject to a customs check regime regardless of their final destination," the statement added, and the plan for a joint EU/UK committee would give the EU a "veto" on which goods would be exempt from tariffs or not.
"This is not acceptable within the internal borders of the United Kingdom," the DUP said.
They expressed concerns Northern Ireland consumers would face increased costs and less choice, and Northern Ireland would also be subject to different VAT arrangements to the rest of the UK.
"Some progress" had been made on democratic consent for the deal, it went on, but the idea of giving the Assembly a vote on the new arrangements that could be won by a "simple majority" violated the Good Friday Agreement, which demands the backing of both unionists and nationalists.
Leader of the Commons and Brexit supporter Jacob Rees-Mogg said it was a "really exciting day today in British politics" as he urged MPs to "rally round this great deal".
But Brexit Party leader Nigel Farage called for it to be rejected by Parliament, saying it would mean "we will not be making our own laws in our own country" and said the treaty "binds us in to other commitments".
Liberal Democrat leader Jo Swinson also condemned the deal as "bad for our economy, bad for our public services, and bad for our environment".
The pro-Remain MP said the "fight to stop Brexit is far from over", adding: "The next few days will set the direction of our country for generations, and I am more determined than ever to stop Brexit."