Britain's ambassador to the EU, Sir Tim Barrow, informed the office of European Council president Donald Tusk on Monday morning of the Prime Minister's plans.
Scotland and Northern Ireland voted to stay in the European Union in the June 23 referendum, while England and Wales voted to leave, resulting in a UK-wide vote of 52 percent for Brexit, and 48 percent against.
Article 50 of the Lisbon Treaty sets out how an EU country might voluntarily leave the union.
TRT World spoke to journalist Myriam Francois who is following the updates from London.
Formal talks between Britain and the EU must then wait for member states to approve more detailed negotiating rules and give an official mandate to European Commission Brexit negotiator Michel Barnier, officials said.
On the EU side of things the European Commission will lead negotiations, but the final agreement will require consent from European Parliament, which consists of hundreds of MEPs from every member of the EU.
The EU said it was ready to begin the negotiations and within 48 hours of the trigger on March 29, Tusk will send the other 27 member states his draft negotiating guidelines, which means that talks could start in May.
Britain has said it wants to agree its divorce and a new relationship with Europe within the two years.
With nationalism and anti-establishment, anti-immigrant sentiment spreading across Western Europe, the European Union leadership in Brussels is anxious to avoid encouraging others in the 28-member bloc to bolt.
At the same time, May faces threats by Scottish nationalists to call a new independence referendum that could break up the United Kingdom.
But the announcement of the date - March 29 - was the first official confirmation of the government's exact timing.