Theresa May has warned the UK faces "uncharted territory" if Parliament rejects her Brexit deal as she vowed to redouble her efforts to win MPs round.
Next week's vote would "definitely" go ahead, she told the BBC, as she promised new safeguards for Northern Ireland and to look at giving MPs more say in shaping future EU negotiations.
The UK's March exit was "in danger" if MPs did not back the deal, she said.
But one Tory Brexiteer said support for leaving without a deal was "hardening".
And one senior Labour figure said she believed a general election may be inevitable "within months" if there was deadlock in Parliament and Mrs May could not get her deal through.
The UK is due to leave the EU on 29 March 2019.
A deal on the terms of the UK's divorce and the framework of future relations has been agreed between the prime minister and the EU - but it needs to pass a vote by MPs in Parliament before it is accepted.
MPs are expected to be asked to vote on it on either the 14 or 15 of January.
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The crunch vote was due to take place in December but was postponed at the last minute as Mrs May faced almost certain defeat amid opposition from many of her MPs, as well as Labour and other parties.
Asked by the BBC's Andrew Marr if the vote would "definitely" go ahead in the second week of January, she replied "yes, we are going to hold the vote".
She said she truly believed hers was a "good deal" for the country and that it was up to its opponents to spell out the alternatives to it.
Media captionTheresa May on Brexit vote timing and her political future
Asked what had changed since last month, she said the EU had agreed to some "changes" and she was continuing to talk to European leaders as she tried to give MPs the "confidence" to support the deal.
She promised to give more detail in three areas in the coming days:
Specific measures for Northern Ireland
A greater role for Parliament in negotiations on the next stage of future UK-EU relations
Further assurances from the EU to address concerns over the Irish border backstop
She said there were a "number of ways" of giving MPs more input in the next phase of the Brexit process, including allowing them a real say in shaping the "mandate for the negotiations for the future relationship".
Mrs May suggested that if her deal was rejected it would embolden both supporters of a no-deal exit and those who want to remain in the EU via another referendum.
"If the deal is not voted on, then we are going to be in uncharted territory," she said. "I don't think anyone can say what will happen in terms of the reaction we see in Parliament.
"What you have is a Labour leadership... which is opposing any deal to create the greatest chaos possible, people who are promoting a second referendum in order to stop Brexit and people who want to see their perfect Brexit... the danger there is we end up with no Brexit at all."
Asked whether she was prepared to stand down as PM and let someone else take over talks over the future relations if Tory MPs demanded it, Mrs May - who survived a vote of no confidence last month - said the party had made it clear they wanted her to "deliver on Brexit and that is what I am working on doing".
However, the DUP, which props up the government, said the fundamental problems with Mrs May's deal had not changed.
Deputy leader Nigel Dodds said: "The backstop remains the poison which makes any vote for the withdrawal agreement so toxic."
The backstop is a position of last resort, to maintain an open border on the island of Ireland in the event that the UK leaves the EU without securing an all-encompassing deal.
Many Conservative MPs continue to believe the deal does not represent the Brexit the country voted for in 2016.
Peter Bone told Sky News the best way to "get on" with Brexit was to leave without a deal,
"If there has been a change it is a hardening of attitudes among MPs to a no deal," he told Sophy Ridge, adding that there was increasing evidence that a no deal outcome was "absolutely OK".
And a succession of other Tory Brexiteers have taken to social media to say "nothing has changed" during the Christmas recess and they remain opposed to the deal.