A deal on the 21-month transition period between March 2019 and the end of 2020 was reached earlier this week, the Euronews said.
The European Council President and chairman of the summit, Donald Tusk, said EU leaders had included the transition offer as they formally adopted their joint negotiating stance on a future trade relationship with Britain.
The guidelines were quickly approved on Friday, paving the way for the next phase of Brexit talks to get underway.
The British prime minister said before leaving Brussels that she believed transition provided certainty for businesses and citizens and that a deal on future UK-EU ties should benefit both sides.
She called for a "new dynamic" in the talks and said she believed there was a new "spirit of cooperation and opportunity".