Already dealt stinging defeats this week from his opponents in Parliament, Johnson suffered a personal blow as his own brother quit the government, saying it was not serving the national interest.
Johnson remained determined to secure an election after lawmakers on Wednesday rejected his attempt to trigger a snap poll. House of Commons leader Jacob Rees-Mogg told Parliament that a vote would be held Sept. 9 on a new motion calling for an election in October.
Johnson's office said the prime minister would appeal directly to the public with a speech later in the day, arguing that politicians must "go back to the people and give them the opportunity to decide what they want."
He called the refusal by Labour Party leader Jeremy Corbyn to endorse an election a "cowardly insult to democracy."
Johnson's determination to lead Britain out of the EU on Oct. 31 faces strong opposition from lawmakers, including members of his own Conservative Party who oppose a no-deal Brexit.
His brother, Jo Johnson, quit the government, saying he could no longer endure the conflict "between family loyalty and the national interest."
Jo Johnson was an education minister in his older brother's government, despite his opposition to leaving the EU without a divorce deal. He said he would also step down from Parliament, the latest in a series of resignations by Conservative moderates opposed to the government's hard-line Brexit stance.
Boris Johnson became prime minister in July after promising Conservatives that he would complete Brexit and break the impasse that has paralyzed Britain's politics since voters decided in June 2016 to leave the bloc and which brought down his predecessor, Theresa May.
After only six weeks in office, however, his plans to lead the U.K. out of the EU are in crisis. He is caught between the EU, which refuses to renegotiate the deal it struck with May, and a majority of British lawmakers opposed to leaving without an agreement. Most economists say a no-deal Brexit would cause severe economic disruption and plunge the U.K. into recession.
Johnson's solution is to seek an election that could shake up Parliament and produce a less troublesome crop of lawmakers. It's a risky gambit: Opinion polls don't point to a clear majority for the Conservatives and the public mood is volatile.
British prime ministers used to be able to call elections at will, but under 2011 legislation fixing elections at five-year intervals, they now need a vote in Parliament to hold an early poll.
On Wednesday, Johnson asked Parliament to back an Oct. 15 election — but Parliament said no. He needed the support of two-thirds of the 650 lawmakers in the House of Commons — a total of 434 — but got only 298, with 56 voting against and the rest abstaining.
Corbyn said Labour, the biggest opposition party, would only vote for an early election if the prospect of a no-deal Brexit was taken off the table.
Labour economy spokesman John McDonnell said the party wanted an election but was still deciding on whether to seek one before the Oct. 31 Brexit deadline, or to wait until Parliament had secured a delay to Britain's departure from the bloc.
"The problem that we have got is that we cannot at the moment have any confidence in Boris Johnson abiding by any commitment or deal that we could construct," he told the BBC. "That's the truth of it. So, we are now consulting about whether it's better to go long, therefore, rather than to go short."
Opposition lawmakers, supported by Conservative Party rebels, are trying to pass a bill that would block a no-deal Brexit on Oct. 31, compelling the prime minister to seek a three-month delay to Britain's departure if no agreement is reached by late October.
The bill was approved by the House of Commons on Wednesday, but faced trouble in Parliament's upper chamber, the House of Lords, where pro-Brexit members planned to defeat it by filibustering — talking until time ran out.
But early Thursday, the Lords agreed to let the bill pass through the chamber by Friday, allowing it to become law on Monday. Johnson plans to suspend Parliament at some point next week until Oct. 14.
Johnson also faces legal challenges to his push to leave the EU come what may on Oct. 31, only 56 days away.
Transparency campaigner Gina Miller, who won a ruling in the Supreme Court in 2017 that stopped the government from triggering the countdown to Brexit without a vote in Parliament, sought a High Court challenge on Thursday to Johnson's plan to suspend Parliament.
Miller, who is supported in her claim by Labour and the governments of Scotland and Wales, argues that sending lawmakers home at a crucial time is unlawful.
"We say that what the prime minister is not entitled to do is to close Parliament for five weeks at such a critical time without justification," her lawyer, David Pannick, told the hearing.
Johnson insists he wants to secure a revised divorce deal to replace the agreement May struck with the bloc, which was rejected by British lawmakers. He told Parliament there was "real momentum" in negotiations with the EU, but European officials deny this and say Britain has yet to produce any concrete proposals.
Pro-Brexit British politicians want a looser economic relationship with the EU than foreseen under May's deal, to make it easier to strike new trade pacts with other countries, including the United States.
U.S. Vice President Mike Pence met Johnson in London on Thursday, saying Washington "is ready, willing and able to immediately negotiate a free trade agreement with the U.K."
But anti-Brexit U.K. politicians fear the Trump administration will demand access to Britain's state-funded National Health Service as part of any deal.
Johnson said at his meeting with Pence that "we will do everything to increase free trade, but the National Health Service is not on the table as far as our negotiations go."
"And we're not too keen on that chlorinated chicken either," he said — a reference to concerns that Britain will have to lower animal hygiene standards as part of a trade deal.