The Attorney General has said 'not one word' of the Good Friday Agreement would be affected by Brexit as a three day High Court case to block it comes to a close.
His comments come in opposition to the argument put forth by a group of MLAs and campaigners bringing a landmark legal bid to halt the UK's planned departure from the European Union.
Victims campaigner Raymond McCord and a cross-party group of MLAs had earlier mounted separate bids to have the process for quitting the EU declared unlawful.
Mr McCord's son Raymond Jr was murdered by loyalist paramilitaries in 1997.
He said, "Justice will be better served for victims by being in Europe. Europe has helped victims and the country as a whole to come together; I believe that would be lost with an exit because the British Government won't support us the same way."
Following the hearing Mr McCord delivered an upbeat assessment of his chances of succeeding.
He said: "I believe, and my legal team believes, he has the power to say Brexit can't go ahead."
The judge overseeing the case at Belfast High Court, Mr Justice Maguire vowed to give immediate consideration to the bid.
With similar litigation due to get underway in London, he is only being asked to rule on issues specific to Northern Ireland at this stage.
Prime Minister Theresa May has announced she will trigger Article 50 of the Lisbon Treaty, the formal process for confirming the UK is to leave, by the end of March 2017.
But during the hearing it was contended that the move is illegal without first securing Parliamentary authorisation.
Even though the June 23 referendum backed Brexit, a 56% majority of voters in Northern Ireland wanted to remain.
Counsel for the Secretary of State insisted the Government is legally entitled to use the royal prerogative to carry out the people's will to get out of the EU.
He described the power as "common currency" in making and withdrawing from international treaties - pointing out that it was also the method used to join the EU.
Rejecting claims that Parliament is being sidestepped in the process, the barrister said the legislative body will be involved in any law changes resulting from Brexit.
According to his case the 1998 Northern Ireland Act created no substantive legitimate expectation that its people will be consulted on before quitting the EU.