All couples in England and Wales will be able to choose to have a civil partnership rather than get married, Theresa May has announced.
The move will provide greater security for unmarried couples and their families, the government said.
And it will address the “imbalance” that allows same-sex couples to enter a civil partnership or get married – a choice denied to mixed-sex couples.
The current system was found in June to be in breach of European law.
The Supreme Court unanimously ruled in favour of Rebecca Steinfeld, 37, and Charles Keidan, 41, from London, who launched their own legal bid to be allowed to have a civil partnership.
The court said that the Civil Partnership Act 2004 was incompatible with the European Convention on Human Rights.
The couple has welcomed the news, but said “legislative action” and a clear timetable was now needed from government.
The Scottish government is also carrying out a consultation on allowing mixed-sex couples to enter into civil partnerships after the ruling.