The Prime Minister revealed that an agreement had been reached with hours to go before a summit of EU leaders in Brussels.
But DUP sources said there had been no change from earlier on Wednesday morning, when the party said it “could not support what is being suggested”.
Mr Johnson tweeted: “We’ve got a great new deal that takes back control — now Parliament should get Brexit done on Saturday so we can move on to other priorities like the cost of living, the NHS, violent crime and our environment”.
The deal is understood to include a watered-down proposal for consent from the Northern Irish assembly on issues affecting the border with Ireland, and a customs regime that will see new checks applied to good crossing the Irish Sea.
Parliament is now expected to vote on the plan on Saturday, the first weekend sitting in 37 years.
Labour said it would push forward a motion for the deal to be subject to a referendum, which the Lib Dems and the SNP indicated they would support.
“As things stand, we could not support what is being suggested on customs and consent issues, and there is a lack of clarity on VAT,” the DUP statement said.
“We will continue to work with the Government to try and get a sensible deal that works for Northern Ireland and protects the economic and constitutional integrity of the United Kingdom.”
Labour leader Jeremy Corbyn said that “from what we know, it seems the Prime Minister has negotiated an even worse deal than Theresa May’s”.
“These proposals risk triggering a race to the bottom on rights and protections: putting food safety at risk, cutting environmental standards and workers’ rights, and opening up our NHS to a takeover by US private corporations,” he said.
“This sell out deal won’t bring the country together and should be rejected. The best way to get Brexit sorted is to give the people the final say in a public vote.”
The pound has hit a five-month high against the US dollar following the announcement from Prime Minister Boris Johnson that a Brexit deal has been agreed with EU officials.
A pound was up 1%, worth 1.2937 dollars, having previously fallen 0.5% earlier on Thursday after the DUP said it would not support the deal in its current form. It was up 0.5% against the euro with a pound worth 1.1129 euros.