The Government is to change the law to enable heterosexual couples to enter into civil partnerships, following a campaign by a Jewish pair.
Ministers said the move, announced at the Conservative Party conference in Birmingham, was an “important step forward for equality”.
It follows a Supreme Court ruling that legislation on civil partnerships, which are currently open only to same-sex couples, was in breach of the European Convention on Human Rights.
In June the Supreme Court unanimously ruled in favour of Rebecca Steinfeld and Charles Keidan, a Jewish couple from London, who mounted a legal challenge to be allowed to have a civil partnership.
Even before the court issued its finding, however, the Government launched a review of the legislation in England and Wales, while the Scottish government has also issued a consultation paper on the subject.
Ms Steinfeld and Mr Keidan welcomed the news that the Government was now committed to act and called on ministers to bring forward legislation as swiftly as possible.
“This is great news and a major step in the right direction, but we will only celebrate when legislation is agreed and the Government confirms the date for when the first different-sex civil partnership can take place,” they said in a statement.
“Change is long overdue. We’ve been struggling for four long years to open civil partnerships to all for the millions of couples like us who want legal recognition and financial protection for their relationship.”
The Government said extending them to opposite-sex couples in England and Wales would provide greater security for those who wanted legal recognition for their relationship but did not want to get married.
In a statement Mrs May said: “This change in the law helps protect the interests of opposite-sex couples who want to commit, want to formalise their relationship but don’t necessarily want to get married.
“As home secretary, I was proud to sponsor the legislation that created equal marriage.
“Now, by extending civil partnerships, we are making sure that all couples, be they same-sex or opposite-sex, are given the same choices in life.”
When civil partnerships were created by Tony Blair’s Labour government in 2004, they were exclusively for same-sex couples, who until that time, were unable to obtain any recognition in law for their relationships.
But after the coalition government under David Cameron acted in 2014 to enable same-sex couples to enter into marriage, the pressure from campaigners to extend civil partnerships to opposite sex couples intensified.
Equalities Minster Penny Mordaunt paid tribute to the efforts of the campaigners and said the Government was committed to bringing in change “as swiftly as possible”.
She said: “This is an important step forward for equality. There are all sorts of reasons why people may choose not to marry.
“By giving couples this option we hope to give them and their families more certainty and security.”