The kick-off date for the Brexit process has been confirmed as Wednesday 29 March.
The UK's ambassador to the EU, Sir Tim Barrow, contacted EU council president Donald Tusk today to provide advance notice of the launch of Brexit talks.
May will contact Tusk directly to launch negotiations.
A spokesperson for May said: "We have always been clear that we will trigger by the end of March and we have met that timetable."
The spokesperson said it is hoped negotiations will start "promptly", adding: "But we fully appreciate it is right that they have the opportunity to agree their position."
Downing Street maintains that Brexit talks will be "a two year process", and said "we are confident that is what we will achieve".
David Davis, the secretary of state for exiting the European Union, 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."
Article 50 was signed into law last week when the Queen granted royal assent for the Brexit bill.