The leaders of the 27 other European Union members states on Sunday approved the terms of a historic Brexit deal with Britain, at a special summit in Brussels.
"EU27 has endorsed the withdrawal agreement and political declaration on the future EU-UK relations," EU Council President Donald Tusk announced on Twitter.
It invites all EU institutions "to take the necessary steps to ensure that the agreement can enter into force on 30 March 2019, so as to provide for an orderly withdrawal".
Britain will leave the EU on March 29.
The statement also gives formal approval to the political declaration on future ties between Britain and the bloc, which covers issues including trade, security and the environment.
"The European Council restates the union's determination to have as close as possible a partnership with the United Kingdom in the future in line with the political declaration," it said.
They thanked chief EU negotiator Michel Barnier for "his tireless efforts".