The UK and the EU have agreed a "flexible extension" of Brexit until 31 October, the BBC reports.
Speaking after five hours of talks at an EU summit in Brussels, European Council president Donald Tusk said his "message to British friends" was "please do not waste this time".
Theresa May said the UK would still aim to leave the EU as soon as possible.
Irish Taoiseach Leo Varadkar said the UK must now hold European elections in May, or leave on 1 June without a deal.
Tusk said "the course of action will be entirely in the UK's hands: they can still ratify the withdrawal agreement, in which case the extension can be terminated."
Mr Tusk said the UK could also rethink its strategy or choose to "cancel Brexit altogether".