Queen Elizabeth II has given Royal Assent to the Brexit bill, clearing the way for Theresa May to start talks to leave the European Union, the BBC reported on Thursday.
The European Union (Notification of Withdrawal) Bill was passed by MPs and peers on Monday.
It allows the prime minister to notify Brussels that the UK is leaving the EU, with a two year process of exit negotiations to follow.
Mrs May says she will trigger the process by the end of the month.
It is unlikely to happen next week to avoid a clash with an informal summit of EU countries.
The meeting will mark the 60th anniversary of the Treaties of Rome, which established the European Economic Community, and in turn became the European Union.