The UK Supreme Court has rejected an attempt to overturn a court ruling in favour of same-sex and unmarried couples adopting.
Northern Ireland health minister Edwin Poots tried to challenge an appeal court's decision that paved the way for gay and lesbian couples to adopt children in the region.
A spokesman for the UK's top court said: "The Supreme Court of the UK has refused permission to appeal the Court of Appeal's decision in this matter."
At present a single gay or lesbian person can adopt in Northern Ireland but a couple in a civil partnership cannot.
A challenge to the legislation was mounted by the Northern Ireland Human Rights Commission, which was backed by an unidentified lesbian woman who wants to enter into a civil partnership and be able to adopt her partner's biological child.
Unmarried couples in Great Britain can apply jointly to be considered for adoption irrespective of sexual orientation. But anyone unmarried in Northern Ireland is only eligible for consideration as an individual.
Those in civil partnerships cannot apply individually or as a couple.
The Commission challenged the law on the grounds that certain provisions were unjustifiably discriminatory to those in homosexual relationships, in contravention of the European Convention on Human Rights.
The Court of Appeal in Belfast ruled in the Commission's favour and against Mr Poots's Department in June.
The Department then applied for permission to appeal to the Supreme Court on a point of law.
The Supreme Court spokesman added: "The Supreme Court issued an order on 22 October 2013 stating that the application did not satisfy the criteria of raising an arguable point of law of general public importance."
The Northern Ireland Human Rights Chief Commissioner Professor Michael O'Flaherty said the Commission brought the case to ensure the best interests of children in Northern Ireland would be protected.
He said: "Unmarried couples, those in same sex relationships and civil partnerships are eligible to be considered to be adoptive parents.
"All of the judgments and today's rejection by the Supreme Court to hear a further appeal confirmed that the law in Northern Ireland was out of step with the United Kingdom's human rights obligations."
In a statement issued tonight, Mr Poots said he was disappointed by the court ruling.
"It is with disappointment that I note that the request for leave to appeal to the Supreme Court has been refused," he said.
"I am currently carefully considering the implications for the Adoption and Children Bill, which is currently being drafted and which I intend to introduce in the Assembly next year.
Gay rights campaigners have accused the minister of wasting public money pursuing his challenge.
John O'Doherty, director of the Rainbow Project, said: "Discrimination on the basis of sexual orientation or marital status is not in the best interest of children. The cost of this case is not just financial but has had a negative impact on the health and wellbeing of countless families.
"Young people in care deserve a loving and caring home and assessments should be left to social workers and other professionals working in this field."