The court ruling came earlier in the year, but now the courts have rejected an appeal by the Health Minister.
In June, the Court of Appeal ruled that the ban based on relationship status was held to discriminate against those in civil partnerships and to breach their human rights.
Northern Ireland was the only part of the United Kingdom where that policy existed.
Now, the law in Northern Ireland is in line with the rest of the UK.
A Department of Health spokesperson said: “Following the Court of Appeal judgement in June 2013, unmarried couples, including same sex couples, and those in a civil partnership may apply to adopt.
Northern Ireland is the only part of the United Kingdom that is not in the process of instituting same-sex marriage.