Prime Minister Theresa May will trigger Britain's exit from the European Union on March 29, a government spokesperson said on Monday.
Downing Street said Britain's ambassador to the EU, Tim Barrow, notified the EU of May's intention verbally.
"The Prime Minister will deliver her letter triggering Article 50 to President (Donald) Tusk on Wednesday (March 29), and deliver a statement to announce the move," a No.10 spokesperson said.
He said that May expected negotiations to "start promptly". Once Article 50 is invoked it will be up to the EU to come back with an early response expected within 48 hours, reported the Independent.
The invocation of the Lisbon Treaty article will formally begin Brexit negotiations.
The move will begin a two-year negotiating period during which the EU and Britain will try to agree the terms of Brexit and reach a separate deal on the shape of their future relationship.
The period can only be made longer by way of a unanimous vote of all European countries' governments. If no deal is reached by the end of the period, Britain will crash out of the EU with no deal and revert to World Trade Organisation rules.
Brexit Secretary David Davis said: "Last June, the people of the UK made the historic decision to leave the EU. Next Wednesday, the government will deliver on that decision and formally start the process by triggering Article 50."
"We are on the threshold of the most important negotiation for this country for a generation.
"The government is clear in its aims: a deal that works for every nation and region of the UK and indeed for all of Europe - a new, positive partnership between the UK and our friends and allies in the European Union," he said.