The prime minister announced her resignation as Conservative Party leader in a statement from Downing Street. May also noted she will continue to lead the government until a successor is chosen.
Earlier this week, the House of Commons leader Andrea Leadsom stepped down amid disagreement with the PM, stating that the government's approach would not deliver on the Brexit referendum's result.
The United Kingdom was initially supposed to leave the European Union on 29 March. A withdrawal deal was reached weeks before this date, but the UK Parliament voted it down, and after a few rounds of negotiations Brussels subsequently moved the deadline to 31 October.