LONDON — Brexit was once again thrown into chaos Tuesday, after Parliament first voted to support Boris Johnson’s withdrawal deal in principle but then, minutes later, rejected his fast-track timetable for passing the necessary legislation.

The yes-no result means that Johnson probably won’t be able to deliver on his “do or die” promise to get Britain out of the European Union by Oct. 31. 

Whether Brexit will be postponed by days, weeks or months remained unclear.

In the House of Commons on Tuesday evening, lawmakers first signaled they did like Johnson’s new Brexit deal, more or less, even grudgingly, by a vote of 329 to 299. 

That was a momentary victory for Johnson — the first time a British prime minister’s withdrawal plan has gotten a parliamentary nod, after repeated defeats in the House of Commons. Duly noted.

But then Parliament voted, 322 to 308, against Johnson’s demand that lawmakers take only three days to read, scrutinize and amend the 115-page legislation.

“So now we face further uncertainty,” Johnson said after that vote.

Ominously, as a clear threat, the prime minister warned that his government would immediately step up preparations to leave the European Union without a deal at the end of October.

But that could be a bluff.

Johnson also said, “One way or another, we will leave the E.U. with this deal, to which this house has just given its assent.”

Johnson also notably omitted any mention of an election in his remarks after the vote, although earlier in the day he suggested that rejecting his timetable would mean that “with great regret the bill will have to be pulled, and . . . we will have to go forward to a general election.”

Following the vote, he suggested more-modest steps forward. He said he would “pause” further Brexit debate in Parliament and wait until the European Union responds to Britain’s request for a delay.

Johnson — who previously said he would “rather be dead in a ditch” than ask European leaders for an extension — was Saturday by law required to request one.

European Commission President Donald Tusk said Tuesday night that he would recommend that the other 27 E.U. leaders accept that request.

E.U. leaders are likely to confer early next week — whether in person or remotely is still unclear — and they probably will offer an extension until the end of January, with the option for Britain to depart earlier if it has approved the deal in the meantime, said diplomats familiar with the discussions.

Before Tuesday’s votes in Parliament, Johnson argued that speed was of the essence: Let’s get it done.

Slow down, warned the skeptics. The British economy is at stake.

Lawmakers complained they were being asked to approve legislation they had not had time to scrutinize or in many cases even read.

The government published its withdrawal agreement bill — the legislation needed to enact the Brexit deal that Johnson negotiated with the European Union — on Monday evening. That was the first chance anyone had to lay eyes on it.

Johnson wanted it sorted in 72 hours.

Ruth Smeeth, a Labour lawmaker who backed the deal in principle but voted against Johnson’s fast-track timetable, said, “All we’re asking for is the opportunity to ensure that the deal that was only presented to us last night works for our constituents and works for my local economy — we need slightly more time.”

Labour leader Jeremy Corybn claimed the latest vote as a refusal by the House of Commons “to be bounced into debating a hugely significant piece of legislation in just two days, with barely any notice and an analysis of the economic impact of this bill. The prime minister is the author of his own misfortune.”

Corbyn made a peace offering, of a sort. He offered Johnson: “Work with us, all of us, to agree a reasonable timetable, and I suspect this House will vote to debate, scrutinize and I hope amend the detail of this bill.”

But Corbyn’s vision of Brexit — remaining closely aligned with the European Union and seeking a second referendum by the people to approve a deal — is anathema to Johnson.

Lucy Powell, another Labour lawmaker, said that “pausing” Brexit “feels like a very churlish reaction to what is a straightforward request” for more parliamentary time.

While lawmakers asked to press ahead on Brexit, House of Commons leader Jacob Rees-Mogg told them that they would be debating the National Health Service on Wednesday and the economy the following day and not sit at all Friday.

Political analysts said lawmakers weren’t wrong to be concerned about the three-day period Johnson proposed for the Brexit legislation.

Hannah White, deputy director of the Institute for Government, an independent think tank, wrote in a post that the timetable proposed was “deeply inadequate.”

“For a constitutional bill which makes probably the most significant changes to the U.K.’s position in the world that the Commons has been asked to consider for decades, it is extraordinary,” she wrote. “The government must know this, but it is asking MPs to agree the timetable or be seen to be thwarting Brexit.” 

“Anyone who claims meaningful legislative scrutiny is possible on this timetable is — at best — misguided,” she added.

Jonathan Tonge, a professor of politics at the University of Liverpool, expressed a similar sentiment.

“It’s an absurdly constrained timetable,” he said. “There hasn’t been a single economic assessment done yet, and the deal is significantly different from” former prime minister Theresa May’s.

When asked about the absence of an economic analysis, Johnson said the agreement would be a “powerful positive shot in the arm for the U.K. economy.”

The deal seeks to leave the E.U. single market, diverge from E.U. customs regimes and tariff schedules, and allow Britain to make independent trade deals around the world. The Johnson exit is a harder Brexit than that envisioned by his predecessor, May.

Johnson’s deal also differs most markedly from May’s over the vexing issue of Northern Ireland, which his deal leaves much more closely aligned to the European Union by effectively putting a border down the Irish Sea.

Some lawmakers pointed out that Parliament spent months debating a bill on how circus animals are treated. Other commentators compared passing Johnson’s Brexit in three days to reading Tolstoy’s phone-book-thick “War and Peace” on the bus ride home.

Michael Birnbaum in Brussels contributed to this report.