Queen Elizabeth II gave royal assent on Thursday to a bill empowering British Prime Minister Theresa May to trigger Article 50 of the EU's Lisbon Treaty and begin the process of leaving the European Union. May has said she will send a letter to the European Council informing them of Britain's decision to leave the bloc by the end of March, following a majority vote for Brexit in last year's referendum.
The House of Commons speaker John Bercow announced the final go-ahead in the parliamentary chamber, prompting cheers from ruling Conservative Party MPs.
"Her Majesty has signified her royal assent," he said.
May's spokesman told a daily briefing: "The legislation now has royal assent.
"We look forward to beginning negotiations when we trigger Article 50 by the end of March," he said.
The queen's signature on the bill allows May to invoke Article 50 at any time, starting a process that will take a maximum of two years unless Britain and its EU partners agree to extend the deadline.
May has said she will address the British parliament to inform lawmakers that she has triggered Article 50, and an initial response is expected from the European Commission within 48 hours.