LONDON—David Davis, the minister in charge of negotiating Britain’s exit from the European Union, resigned unexpectedly Sunday night, according to someone familiar with the decision, likely heralding a further period of turmoil for the trouble-prone government of Prime Minister Theresa May.
The resignation by a prominent minister who campaigned for Britain to leave the EU follows a cabinet meeting on Friday in which a plan for Britain’s future relationship was finally hammered out, 25 months after a referendum vote to leave...