Those personal qualities have come into play at a pivotal moment as Britain hurtles toward its March 29 exit with a government in stalemate.

“He is a law unto himself,” said Bobby Friedman, the author of a biography of Mr. Bercow, recalling the speaker’s decision on Jan. 9 to allow Parliament to amend a government business motion on Brexit. Business motions give the executive power to determine what happens in Parliament and when, and have not been considered changeable by Parliament.

“From a political geek’s point of view, it was pretty astonishing,” Mr. Friedman said of Mr. Bercow’s decision. “He said, ‘I’ll do what I like.’ If anyone else was speaker, it would have been incredibly surprising. With him, not particularly.”

Even in the hyper-loquacious environment of British politics, Mr. Bercow stands out for his love of ornate language and withering insult.

“He could never say, ‘It’s great to see you’ ”; instead he would say, ‘It gives me inestimable pleasure to meet you for the finest condiments created by Mrs. Twinings,’ ” a colleague told Mr. Friedman, his biographer. A sitting lawmaker told The New York Times in 2013, “It’s as if he goes to bed every night, reads a thesaurus, inwardly digests it and then spews it out the next day.”

Occasionally, when a fellow politician was speaking, he would cry out, “Split infinitive!”

Mr. Bercow has made a career out of annoying his conservative colleagues. Some are still seething over his decision not to wear the traditional speaker’s regalia, including wig and knee-breeches, which he said created “a barrier between Parliament and the public.”