Mrs May is expected to make a statement to the House of Commons shortly after invoking Article 50.
The meeting will be used to agree the guidelines for the EU's negotiating team headed by Michel Barnier.
Britain is slated to trigger the two-year period of its exit from the European Union on March 29, with the talks starting for real in May.
European Council president Donald Tusk confirmed that he will present draft Brexit guidelines to the remaining 27 member states within 48 hours of notification.
"The sooner we reach a deal on an orderly withdrawal, the sooner we can prepare for the future relationship", he said today.
Talking about the rights of European Union citizens, Bernier acknowledged that the issue was complex and would take several months to sort out, but said ending the current state of uncertainty for up to 4 million people should be a priority for both the European Union and the UK.
"Our main priority for the negotiations must be to create as much certainty and clarity as possible for all citizens, companies and member states that will be negatively affected by Brexit".
Mr Tusk said his priority was making sure the "divorce" was the "least painful" for the EU.
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EURACTIV reports from the streets of London on the public's views on Brexit.
However, the man who will lead the Brexit negotiations for the European Commission added there would be no penalty fee for the country leaving the union and the United Kingdom would not be asked to pay for anything it had not previously signed on for.
The possibility of a transitional deal to cover unresolved issues like trade tariffs and immigration after Britain leaves in two years promises to be one of the key sticking points in the Brexit negotiations.
Brexit will put British patients at the "back of the queue" for vital new drugs, the Government has been warned - forcing them to wait up to two years longerA medicines regulator has raised the alarm over a likely decision to pull out of the European Medicines Agency (EMA), as well as the EU itself. ealth Secretary Jeremy Hunt dropped the bombshell, when he said he expected the United Kingdom would quit the EMA - because it is subject to rulings by the European Court of Justice.
But the actual Brexit talks will not start for around three or possibly more weeks after the summit, when ministers will formally give a mandate to Barnier, EU officials said.
"We will be particularly attentive, in these negotiations, to the consequences of the UK's decision to leave the Customs Union, and to anything that may, in one way or another, weaken dialogue and peace", Barnier said.
Scottish First Minister Nicola Sturgeon has said she wants a second referendum on Scottish independence after the terms of the deal are known and before Brexit takes effect in the spring of 2019.
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