She also repeated arguments against a second referendum - another people's vote on Brexit. May said the people already voted for Brexit and the job of her government and Parliament is to deliver it. A second referendum, she warned, "could damage social cohesion by undermining faith in our democracy".
May said she thought progress was possible on the most contentious element of the withdrawal deal - the so-called "Irish backstop," an insurance policy meant to prevent the re-emergence of a hard border on the island of Ireland after Brexit. An open border was a key part of the 1998 Good Friday Agreement that brought an end to decades of conflict in Northern Ireland.
May said she would consult MPs "to consider how we might meet our obligations to the people of Northern Ireland and Ireland in a way that can command the greatest possible support in the House."
"And I will then take the conclusions of those discussion back to the EU," she said.
But how much room to manoeuver is there on the EU side of the table?
European leaders have repeatedly said the deal May presented to Parliament last week, painfully negotiated over months and months, was the best they could offer. And they have been reluctant to resume any discussions until Britain can present a more united front.
Germany Chancellor Angela Merkel over the weekend put some of the onus back on the EU. "We have a responsibility to shape a divorce process so that people don't shake their heads at us in 50 years time and say why weren't they in a position to make a compromise?" she said.
Polish Foreign Minister Jacek Czaputowicz floated the idea of limiting the Irish backstop to five years.
"I don't know if it's feasible, if Ireland is ready to put forward such a proposal, but I have an impression that it might unblock the negotiations," he told the BBC.
Speaking in Brussels, Irish Foreign Minister Simon Coveney dismissed the idea.
"He mentioned that issue in Dublin in December when he visited," Coveney told reporters. "I made it very clear that putting a time limit on an insurance mechanism, which is what the backstop is, effectively means that it's not a backstop at all. I don't think that reflects EU thinking in relation to the withdrawal agreement."
May didn't mention any specific limit on the backstop in Parliament.
In fact, the biggest news in her remarks was the announcement that the three million EU citizens living in Britain would not need to pay a planned 65 pound fee to apply for residency status after Brexit.
MPs complained that she was bringing nothing new. Several commented that May seemed out of ideas - and appeared more defeated than defiant.
"It's like last week's vote never happened. Plan B is Plan A," tweeted Sarah Wollaston, a Tory MP who supports a second referendum.
"The Government still appears not to have come to terms with the scale of the defeat in the House of Commons last week," said Jeremy Corbyn, leader of the opposition Labour Party. "The Prime Minister seems to be going through motions of accepting the result but in reality is in deep denial."
"It really does feel a bit like groundhog day," Corbyn said.
Going forward, Corybn said Parliament will have more of a say over how Brexit unfolds.
"Today heralds the start of a democratic process where this House will debate amendments that will determine how we navigate Brexit," said the Labour leader.
Corbyn has refused to take part in cross-party talks unless May removes the possibility of a no-deal Brexit.
But rather than woo opposition MPs and risk splitting her own party, May seems to have calculated that it's better to try and win over the rebels in her Conservative Party - more than a third of Tories voted against Plan A - and the Democratic Unionist Party of Northern Ireland that props up her minority government.
Many political commentators think Britain will seek to postpone Britain's departure from the EU beyond the March 29 deadline by seeking an extension to Article 50.
German Foreign Minister Heiko Maas told reporters in Brussels that EU ministers were keen to get a sense of direction from London. "We know what London doesn't want, now we must at last find out what they want," he said.
He also stressed it was important that there wasn't a hard border in Ireland, while making reference to a bomb explosion in the center of Londonderry, Northern Ireland, on Sunday.
"Europe is a peace project, and Europe cannot do anything which leads to conflicts breaking out again in a part of Europe where they have long since been laid to rest," he said.
"It's a very sensitive issue and therefore it's an issue which in the discussions to come I cannot imagine there will be much change."
