U.K. lawmakers passed crucial legislation in favor of delaying Brexit on Wednesday. The House of Commons ensured the vote by a tally of 327 to 299.
Johnson, who became prime minister in July, had pledged that the U.K. would leave the EU by the Halloween deadline "come what may." He has said that he would put forward a motion to hold a snap general election if the legislation passes on Wednesday.
The new vote comes after a crunch moment in Parliament Tuesday when a majority of lawmakers backed a plan to take control of parliamentary business. This was seen as the first step in a bid to stop a potentially damaging no-deal Brexit, which was also a major blow for Johnson and his government.
A no-deal departure from the EU worries many Members of Parliament (MPs) on both sides of the "Remain" and "Leave" camps as it would mean an abrupt, overnight departure from the EU on October 31 with no transition period.
Pro-Brexit Johnson had argued that keeping a no-deal departure on the negotiating table strengthened the U.K.'s position in any last-ditch attempts to get the EU to amend the Brexit deal on offer.
If the legislation to stop a no-deal passes Wednesday evening, it would essentially force the prime minister to ask the EU for another delay to Brexit, to January 31 2020, if there is no deal in place or if a deal has not been agreed in Parliament by October 19. The EU would have to agree to a delay and the bill would also have to be ratified by the largely pro-EU House of Lords later this week.
If Johnson does call a snap election, two-thirds of Parliament would have to agree to holding a vote — unless Johnson tries to bring forward new legislation to hold a vote with just a simple majority, although this is seen as an unlikely possibility. There is uncertainty over the timing of any potential national vote too.
— CNBC's Jasmine Kim contributed to this report.