The bill implementing Britain's exit deal with the European Union officially became law on Thursday ahead of the country's departure from the bloc next week.
The legislation passed its final parliamentary stage on Wednesday, after more than three years of bitter wrangling over how, when and even if Brexit should take place.
Queen Elizabeth has now given it Royal Assent, the leader of the House of Commons, Jacob Rees-Mogg, said on Twitter.
Britain is due to leave the bloc at 11pm GMT on January 31.
A consent vote in the EU Parliament will take place on January 29.
Prime Minister Boris Johnson is expected to formally sign the Withdrawal Agreement in the coming days.
On Wednesday British politicians overturned changes to the government’s Brexit bill, removing a promise to reunite child refugees with their families in the UK.
As the bill goes through its final stages before becoming law, the House of Commons removed five amendments inserted into the Withdrawal Agreement Bill by the unelected House of Lords.
The promise was made in 2018 by former British prime minister Theresa May, but it was removed from the Brexit legislation after Prime Minister Boris Johnson’s Conservatives won a big parliamentary majority in an election last month.
Mr Johnson's government says it intends to continue resettling child migrants in Britain after the country leaves the EU but the issue does not belong in the EU withdrawal bill, which sets out the terms of Britain’s departure from the 28-nation bloc.