Theresa May says she understands "the voice of the country" on Brexit, despite her own vocals wavering.
Battling a sore throat at Prime Minister's Questions, she insisted the UK can still leave the EU with a "good deal" and said she would vote later to rule out a no-deal exit on 29 March.
But Mrs May warned MPs they faced "hard choices" having rejected her deal for a second time.
Jeremy Corbyn called on the PM to change course after the defeat.
He said the deal had been "decisively rejected" and it was time for the prime minister to change her red lines.
After the Commons rejected Mrs May's Brexit deal by 149 votes on Tuesday, the EU has warned the risk of a "disorderly" Brexit has never been higher.
Its chief negotiator Michel Barnier said the EU "cannot go any further" in trying to persuade MPs to back the agreed terms of exit and the UK had to break the impasse.
MPs will vote at 19.00 GMT on whether to block the UK from leaving the EU without an agreement later this month.
Wednesday's vote only applies to the 29 March deadline and would not rule out the prospect of a no-deal exit later this year, if Parliament is ultimately unable to agree a way forward.
May and Corbyn clash over Brexit deal
The Labour leader said the prime minister was in denial about her own deal's lack of support after MPs rejected it by a margin of 149 votes.
He suggested his alternative plan to remain in a customs union was "the only show in town".
"Isn't it time she moved on from her red lines and faced the reality of the situation she has got herself, her party, this parliament and this country into?" he said.
But dismissing calls from Tory MPs to embrace a no-deal exit now, Mrs May said her deal remained the best way to honour the 2016 referendum result.
"I may not have my own voice but I understand the voice of the country," she said.
"I believe we have a good deal. No deal is better than a bad deal but I have been working for us to leave on 29 March and leave with a good deal."
What's the response from the EU?
The EU has urged the UK to take "responsibility" for its actions.
"Again the House of Commons says what it doesn't want," Mr Barnier told the European Parliament. "Now this impasse can only be solved in the UK.
The EU, he suggested, had gone "as far as it possibly can" to satisfy MPs' concerns over the agreement, particularly in relation to the backstop, an insurance policy to stop a hard border on the island of Ireland.
"If the UK still wants to leave the EU in an orderly manner, this treaty is, and will remain, the only treaty possible," he said.
What are MPs voting on later?
MPs will vote on a government motion, which says the Commons "declines to approve leaving the European Union without a withdrawal agreement and a framework on the future relationship on 29 March".
Mrs May has said Tory MPs will get a free vote.
That means ministers and MPs can make their own mind up rather than following the orders of party managers - an unusual move for a vote on a major policy.
The no-deal debate will begin after Chancellor Philip Hammond's Spring Statement economic update.
Leaving the EU in 16 days' time remains the UK's default position under the law, unless talks are extended.
If a no-deal exit is rejected, MPs will vote on Thursday on delaying Brexit by extending Article 50 - the legal mechanism that takes the UK out of the EU.
The EU has said it would need "a credible justification" before agreeing to any extension. Such a move would have to be agreed by every member state.
Although the PM managed to convince about 40 Tory MPs to change their mind, it was not nearly enough to overturn the historic 230 vote defeat she suffered on the same deal in January.
Despite Tuesday's defeat, the BBC News political editor Laura Kuenssberg said, there were ministers who believed it could still ultimately prevail as other options gradually fell by the wayside due to lack of parliamentary support.
What alternatives are being discussed?
Labour wants no-deal to be "taken off the table" and is likely to back an amendment - a legislative tool - tabled by MPs Jack Dromey and Caroline Spelman ruling out the UK leaving without an agreement at any stage in the process.
Shadow business secretary Rebecca Long-Bailey told the BBC that Parliament would increasingly "set the agenda" if the government was not in control of events.
She said No 10 should consider giving MPs a free vote on the full range of options for the UK's relationship with the EU - including Labour's own plans for a customs union.
What isn't clear is how the prime minister actually intends to dig herself out of this dreadful political hole.
Some of her colleagues around the Cabinet table think it shows she has to tack to a closer deal with the EU.
Some of them believe it's time now to go hell-for-leather to leave without an overarching deal but move to make as much preparation as possible, and fast.
Other ministers believe genuinely, still with around two weeks to go, and an EU summit next week, there is still time to try to manoeuvre her deal through - somehow.
Among other proposals which could be discussed on Wednesday is a plan for the UK to leave without a formal agreement but with a number of safeguards to minimise economic disruption.
The plan, known as the Malthouse compromise, is backed by Brexiteer members of the European Research Group of Tory MPs, as well as the DUP and former Remain ministers like Nicky Morgan and Damian Green.
It would see the controversial backstop replaced by alternative arrangements, an extended pay-as-you-go transition period and a series of "standstill" arrangements for various industries until the end of 2021.
Amid reports Brexiteer ministers have been granted a free vote on this proposal, Tory MP Steve Baker told BBC News the plan - which would see Brexit delayed until 22 May - was "eminently reasonable".
But Tory former minister Nick Boles said this would amount to a no-deal exit and the EU would not agree to it.
What would UK do in no-deal scenario?
Ahead of the no-deal Commons vote, the government announced that most imports into the UK would not attract a tariff in the event of a no-deal Brexit.
Under a temporary scheme 87% of imports by value would be eligible for zero-tariff access - up from 80% at present. Tariffs would be maintained to protect some industries, including agriculture.
The government also announced it will not introduce any new checks or controls, or require customs declarations for any goods moving across the border from Ireland to Northern Ireland if the UK leaves the EU without a deal.
The decision to drop all checks to avoid friction at the UK's land border with the EU will be temporary while longer term solutions are negotiated.