But, if Parliament votes against May's embattled template to leave the bloc, the EU will support a shorter delay until April 12. This is designed to allow the U.K. time to get the deal through or indicate another way forward.
"This is perhaps the last chance for Britain to say what it wants for the future," Belgium's Prime Minister Charles Michel told reporters on Friday.
"More than ever, this is in the hands of the British parliament," Michel said, as he arrived for the second day of an EU summit overshadowed by talks over Britain's departure.
May, who had asked to be able to delay Britain's departure until June 30, said British lawmakers now faced a "clear choice."
They could either support her Brexit deal, deliver on the referendum result and exit the EU in an "orderly manner" or face the prospect of having to stand candidates in the European Parliamentary elections three years after a small but clear majority voted for Brexit.
On Thursday, EU leaders spent seven hours discussing a host of options regarding Brexit, saying that while they regret the country's decision to leave, they are eager to move on with the process.
Eventually, the bloc decided a May 22 departure date would apply if Parliament rallies behind the prime minister next week. Otherwise, Britain must decide whether to offer a new plan or leave the EU without a deal on April 12.
"In case of no vote (in Parliament)… it will guide everybody to a no-deal for sure," French President Emmanuel Macron told reporters on Thursday.
"This is it. We are ready," Macron said.
The French premier reportedly told EU leaders in the room on Thursday that before coming to Brussels he had thought May only had a 10 percent chance of winning a third meaningful vote.
But, after listening to the prime minister speak on Thursday, he had cut his estimate to just 5 percent, Reuters reported on Friday, citing sources familiar with the discussions.
Many market participants are fearful a no-deal Brexit, sometimes referred to as the "cliff-edge" scenario, could hammer both economic growth and jobs in the world's fifth-largest economy.
"If next week, there is no vote or the vote is negative, then we have already agreed that the cliff-edge then becomes, in a sense, April 12," Latvian Prime Minister Krisjanis Karins told CNBC's Willem Marx in Brussels on Friday.
When asked whether he had the impression that EU leaders were now fully prepared for a no-deal scenario, Karins replied: "How can you prepare for something terrible?"
"We don't want this but we realised a while ago that we had better be prepared… and this has probably happened in all member states."
Goldman Sachs said the likelihood of a no-deal Brexit had increased to 15 percent from 5 percent, Reuters reported, citing a research note published Friday. The U.S. investment bank cut the chances of May's deal passing to 50 percent, down from 60 percent.