After the meeting, European Union commission president Jean-Claude Juncker said that the agreement was the "best possible deal for Britain", before adding he felt "deep sadness" towards Britain's departure from the EU.
Meanwhile the Democratic Unionist Party, which props up her minority government, threatened towithdraw their support for the Conservatives if the deal is agreed by the United Kingdom parliament.
He told the BBC's Andrew Marr Show: "It's not possible to rule out anything, and that's why all of us have to do is say, what do your constituents actually want in this situation, and we have to work out what's in the national interest, and it's all about the balance of risks".
Negotiations have been going for 17 months regarding Britain's departure from the EU.
Mrs May has appealed to the British public to get behind the agreement - saying that although it involved compromises, it was a "good deal that unlocks a bright future for the UK".
Her comments came as her former Brexit Secretary Dominic Raab said staying in the European Union would be better than leaving under Mrs May's deal.
Over the last day, May has been accused by Labour of abandoning Gibraltar after Spain's government claimed to have secured the country's greatest diplomatic victory for 300 years.
Tom Brake, the Liberal Democrat's Brexit spokesman, said: "The prime minister has caved in once again".
The Spanish government announced on Saturday (24 November) that it would back the deal after striking a last-minute agreement to ensure any agreement for the future relationship with the United Kingdom will not automatically apply to Gibraltar.
Taoiseach Leo Varadkar has said the withdrawal agreement is the only Brexit deal on the table.
The U.K. Telegraph reported that the British government has conceded in writing that no part of any future trading agreement can apply to Gibraltar without the agreement of the Spanish government - leading to fears that the Spanish may use that power to extract a deep range of concessions on issues such as taxation and fishing. The agreement leaves Britain outside the European Union with no say but still subject to its rules and the obligations of membership at least until the end of 2020, possibly longer.
Earlier this week, May underscored in an open letter to the nation that she would campaign "heart and soul" to get her Brexit deal through Parliament, even amid stiff opposition within and beyond her own party.
The EU's chief negotiator Michel Barnier said the deal was a "necessary step" to prepare for the next phase of negotiations which the Government hopes will result in a wide-ranging free trade agreement.
While UK MPs present a possible roadblock to concluding the deal, the European parliament's president, Antonio Tajani, predicted its members would sign-off the deal by February.
"The public would expect parliament to vote on the deal".
May insists her deal delivers on the things that matter most to pro-Brexit voters - control of budgets, immigration policy and laws - while retaining close ties to the U.K.'s European neighbors.
She praised the deal struck "in an extremely hard situation, in a situation without any precedence because we haven't had it before that a European country leaves the EU".