In June, the UK voted to leave the EU — a result that sent shockwaves through Northern Ireland, where 56% of the electorate backed Remain.
Following the result, Raymond McCord, the father of a loyalist paramilitary victim, and a cross-party group of MLAs mounted separate cases aimed at having the Brexit process declared unlawful.
But Mr Justice Maguire rejected claims the Government could not use royal prerogative powers to begin withdrawal without an Act of Parliament.
Throwing out all grounds of challenge, he said: “The court is not persuaded, for the purpose with which this judicial review is concerned, prerogative power has been chased from the field.”
Undeterred, Mr McCord took his challenge to the Supreme Court in December, with a ruling expected in the new year.
Three groups of citizens also brought a case before the High Court of England and Wales to challenge the Government’s interpretation of the law.
On November 3, the court ruled that the UK required a vote in Parliament before formally starting the process to leave the EU. A Supreme Court ruling is expected in early January.
Prime Minister Theresa May is set to trigger Article 50 of the Lisbon Treaty — the formal process for withdrawing from the EU — by the end of March 2017.