Theresa May has suffered three Brexit defeats in the Commons as she set out to sell her EU deal to sceptical MPs.
Ministers will be forced to publish the government's full legal advice on the deal after MPs found them in contempt of Parliament for issuing a summary.
And MPs backed calls for the Commons to have a direct say in what happens if her deal is rejected next Tuesday.
Theresa May said MPs had a duty to deliver on the 2016 Brexit vote and the deal on offer was an "honourable compromise".
Addressing the Commons at the start of a five-day debate on her proposed agreement, Theresa May said Brexit divisions had become "corrosive" to UK politics and the public believed the issue had "gone on long enough" and must be resolved.
MPs will decide whether to reject the terms of the UK's withdrawal and future relations with the EU on Tuesday 11 December.
In other Brexit-related developments:
- Former UKIP leader Nigel Farage has quit the party in protest at its direction
- The BBC said it had been unable to agree a format for a Brexit debate between Theresa May and Jeremy Corbyn following discussions with the parties
- The pound briefly fell to 18-month lows after the government lost the contempt vote
- Former Bank of England Governor Mervyn King likens Brexit deal to appeasement
- The UK should be able to unilaterally cancel its withdrawal from the EU, according to a top European law officer
What was the legal advice row?
The Commons supported a motion demanding full disclosure of the government's legal advice, by 311 votes to 293.
The move was backed by six opposition parties, while the Democratic Unionists, which have a parliamentary pact with the Conservatives, also voted against the government.
It came after Attorney General Geoffrey Cox published a summary of the advice on Monday and answered MPs questions for three hours - but said that full publication would not be in the national interest.
Labour had accused ministers of "wilfully refusing to comply" with a binding Commons vote last month demanding they provided the attorney general's full and final advice.
After Labour demanded the advice should be released ahead of next Tuesday's key vote on Theresa May's deal, Commons Speaker John Bercow said it was "unimaginable" this would not happen.
In response, Commons Leader Andrea Leadsom said she "would respond" on Wednesday but would ask the Commons Privileges Committee to consider the constitutional repercussions.
An attempt by ministers to refer the whole issue, including the government's conduct, to the committee of MPs was earlier defeated by four votes.
The privileges committee will now decide which ministers should be held accountable and what sanction to apply, with options ranging from a reprimand to the more unlikely scenario of a minister being suspended from the Commons.
Lib Dem leader Sir Vince Cable said the result left the government "on the ropes", adding: "Theresa May's majority has evaporated, and the credibility of her deal is evaporating with it."
MPs seek to influence Brexit process
The prime minister suffered a further setback on Tuesday as MPs backed, by 321 votes to 299, changes to the parliamentary process should the Commons vote down her deal next week.
If that happens, the government has 21 days in which to return to the House and set out what it plans to do next.
But Tory Dominic Grieve's motion means that instead of MPs being confined to merely taking note of what the government tells them, the Commons would be able to exert more influence by voting on what they wanted the government to do as well.
Tuesday's vote, in which 26 Tory MPs rebelled, could potentially tilt the balance of power between government and Parliament if, as expected, MPs push for a "Plan B" alternative to Theresa May's deal and also seek to prevent any chance of a no-deal exit.
Mr Grieve, who has expressed support for another Brexit referendum, told Channel 4 News he was not seeking to "guarantee a particular outcome" if Theresa May's deal went down.
But he said it would "allow the UK time to consider its options" - including potentially re-starting negotiations with the EU or giving the public the final say.
What did the PM say?
As she sought the backing of the Commons for her Brexit deal, the prime minister said she was confident the UK would enjoy a "better future" outside the European Union.
She said the "honourable compromise" on offer was "not the one-way street" many had portrayed it to be and that the EU had made it clear that the agreement would not be improved on.
"I never said this deal was perfect, it was never going to be. That is the nature of a negotiation," she said.
"We should not let the search for a perfect Brexit prevent a good Brexit... I promise you today that this is the very best deal for the British people and I ask you to back it in the best interest of our constituents and our country."
But Labour leader Jeremy Corbyn said it was a bad deal for the UK and Labour would seek a vote of no confidence in Theresa May if she could not get it through Parliament.
"This House will make its decision next Tuesday," he said. "I hope and expect this House will reject that deal.
"At that point, the government has lost the confidence of the House. Either they have to get a better deal from the EU or give way to those who will."
Ex-foreign secretary Boris Johnson dismissed the deal as a "paint and plaster pseudo-Brexit" and said its supporters would be "turning their backs" on the 17.4 million Leave voters.
"If we try to cheat them now, as I fear we are, they will spot it and will never forgive us," he said.