The maneuver sets up a showdown with lawmakers in the coming weeks and thrusts the country into further political uncertainty as the Oct. 31 Brexit deadline looms.

Details: Parliament is scheduled to come back from summer break on Tuesday for two weeks and then break up again for annual political party conferences. It was then scheduled to reconvene around Oct. 9.

But now, Parliament will resume on Oct. 14 instead, leaving just over two weeks for lawmakers to fashion a deal with the E.U. to soften the exit. A departure without such terms could plunge the country into a recession, critics say. Here’s our explainer of what comes next.

Analysis: Mr. Johnson’s surprise gamble revealed another side of the bumbling, mischievous leader: a pugnacious, ruthless tactician.