Sons and daughters of any future UK monarch will have equal right to the throne, after Commonwealth leaders agreed to change succession laws.
The leaders of the 16 Commonwealth countries where the Queen is head of state unanimously approved the changes at a summit in Perth.
It means a first-born daughter of the Duke and Duchess of Cambridge would take precedence over younger brothers.
The ban on the monarch being married to a Roman Catholic was also lifted.
Under the old succession laws, dating back more than 300 years, the heir to the throne is the first-born son of the monarch. Only when there are no sons, as in the case of the Queen’s father George VI, does the crown pass to the eldest daughter.
The succession changes will require a raft of historic legislation to be amended, including Britain’s 1701 Act of Settlement, the 1689 Bill of Rights and the Royal Marriages Act 1772.
The change to the Royal Marriages Act will end a position where every descendant of George II is legally required to seek the consent of the monarch before marrying.
In future, the requirement is expected to be limited to a small number of the sovereign’s close relatives.
Announcing the succession changes, UK Prime Minister David Cameron said they would apply to descendents of the Prince of Wales. They will not be applied retrospectively.
“Put simply, if the Duke and Duchess of Cambridge were to have a little girl, that girl would one day be our queen,” he said.
“The idea that a younger son should become monarch instead of an elder daughter simply because he is a man, or that a future monarch can marry someone of any faith except a Catholic – this way of thinking is at odds with the modern countries that we have become.”
Australia’s Prime Minister Julia Gillard said it was an extraordinary moment: “I’m very enthusiastic about it. You would expect the first Australian woman prime minister to be very enthusiastic about a change which equals equality for women in a new area.”
She said the changes appeared to be straightforward. “But just because they seem straightforward to our modern minds doesn’t mean that we should underestimate their historical significance, changing as they will for all time the way in which the monarchy works and changing its history.”
But the campaign group Republic – which wants an elected head of state in Britain – said “nothing of substance” had been changed.
“The monarchy discriminates against every man, woman and child who isn’t born into the Windsor family. To suggest that this has anything to do with equality is utterly absurd,” spokesman Graham Smith said.