DUP deputy leader Nigel Dodds last night said it would now be "very unwise" to predict when the UK will leave the EU.
Mr Dodds' comments made the comments just hours after 11 Supreme Court judges agreed unanimously that Mr Johnson broke the law when he asked the queen to prorogue Parliament.
Delivering the Supreme Court judgment Lady Hale said: 'The decision to advise Her Majesty to prorogue was unlawful because it had the effect of frustrating or preventing the ability of Parliament to carry out its constitutional functions. The effect upon the fundamentals of our democracy was extreme. No justification for taking action with such an extreme effect has been put before the court."
Mr Dodds said the "shenanigans" in the Commons had weakened the prime minister's hand in negotiations.
He said that despite the decision "we do still need a deal with the EU to be negotiated".
"This is just another step on the way and there will be many more twists and turns in the saga," he said.
"I think it would be very unwise for anyone to predict, never mind the end of October, what's going to happen next week. I think we're in unchartered territory."
He added: "There still needs to be a negotiation with Europe. Some of the language we are hearing out of Brussels about their intransigence is not very encouraging".
Earlier party leader Arlene Foster said the DUP - which has a confidence-and-supply agreement with the government - said it had "always respected the principle of the separation of powers upon which our constitutional law is founded. Therefore the judgment of the Supreme Court has to be respected".
Following the findings, the Northern Ireland parties responded, with some calling for the prime minister to resign.
Sinn Fein vice-president Michelle O'Neill said the finding demonstrated that the British government had " lost control of its own agenda".
"What this demonstrates for me is more of the chaos, the dysfunction, the mess that is happening and unfolding day on day in Westminster," she said.
"It is a constitutional crisis, we have been saying that for some time and I believe this is another one of those meltdown moments for this British Government".
SDLP leader Colum Eastwood said Mr Johnson was ""unfit for the office he holds".
"Today's ruling at the Supreme Court confirms that he acted unlawfully to undermine the democratic accountability and scrutiny of his Government at a critical time for these islands," he said.
"Full scrutiny of this Government and its plans for a hard Brexit must now be restored and challenged immediately. Johnson must be removed from office and Brexit called to a halt.
"The best way to do that is through an election".
Alliance leader Naomi Long said parliamentary scrutiny at "this crucial time in the Brexit process is vital"
"It is clear now the prime minister and his inner circle acted unlawfully," she said.
Ulster Unionist leader Robin Swann described the judgment as "devastating" for the government adding that it "sends a warning to all that nobody should play fast and loose with Parliamentary process".
"The Johnson government are not the only ones to engage in that.
"The decision of the Supreme Court must be respected so that we can return to some semblance of normality, if that is possible in the current climate".
Green Party leader Clare Bailey said the decision by the Supreme Court had cut across the "Westminster chaos".
"It's imperative that Parliament is re-convened and all efforts are directed towards preventing a no-deal Brexit," she said, calling for a "people's vote".
