A summit of EU member states to discuss Brexit is be held on 29 April, a month after the UK triggers Article 50.
The meeting will be used to agree the guidelines for the EU’s negotiating team headed by Michel Barnier.
European Council president Donald Tusk said the priority would be giving “clarity” to EU residents, business and member states about the talks ahead.
Prime Minister Theresa May will officially notify the EU of the UK’s intention to leave on 29 March.
She told her cabinet on Tuesday that triggering Article 50 would be an “historic event” and the start of a “bold new chapter… as a prosperous open and global nation”.
The letter which she will send to Mr Tusk, will be “one of the most important documents in the country’s recent history” and it will set the tone for a new relationship with the EU, she told her senior team of ministers.
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April’s meeting, which the UK will not attend, will be held just days after the first round of voting in the French presidential election.
Mrs May has said she hopes that talks will get under way as soon as possible although it is thought that they will not begin in earnest until after April’s meeting and the final outcome of the French contest is known on 7 May.
In a statement, Mr Tusk said he regretted but respected the UK’s decision to leave the EU and wanted the “process of divorce” to be as “painless as possible” for the European Union.
“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, as well as our important partners and friends around the world like Japan,” he said.
British ministers have said the EU’s draft guidelines, which are expected to be published within 48 hours of Article 50 being triggered, will be a “very important” moment of “choreography” in the Brexit process.
Once talks start, they are expected to focus initially on the rights of EU nationals living in the UK and Britons living on the continent as well as what, if any, payments the UK will have to make to the EU’s budget to cover current and future liabilities.
Mr Barnier, a former European Commission official, has called for talks to be completed by October 2018 to give time for any agreement to be ratified before the UK leaves, expected on March 29 2019 under the two-year Article 50 process.
Within days of April’s meeting, he is expected to make recommendations to EU leaders how the talks should be structured to achieve this.
Brexit: EU summit on 29 April to discuss way ahead}