The former Prime Minister said that if MPs “don't want no deal they have to vote for a deal” and argued Parliament would be guilty of “most egregious con trick” if they failed to endorse Mr Johnson’s plans.
She also said there should not be a second referendum "simply because people don't like the result of the first".
Her comments came just an hour before Boris Johnson suffered a narrow defeat in a vote over the Letwin amendment, which means the meaningful vote will now take place next week.
"I intend to rebel against all of those who don't want to vote to deliver Brexit," Mrs May said.
Making reference to the three occasions she failed to get her own withdrawal agreement approved by MPs, Mrs May told Mr Johnson she felt a "distinct sense of Déjà vu" about the debate.
During her tenure in Number 10 Mrs May said that no Prime Minister could accept the idea of a customs border down the Irish Sea between Great Britain and Northern Ireland.
Mrs May’s support for Mr Johnson’s deal comes despite his critics claiming that his version of the withdrawal agreement does just that.
READ MORE FROM YAHOO NEWS UK:
Boris Johnson news - live: Knife-edge vote expected on Letwin amendment that will derail PM's Brexit plan
Another former Tory leader Michael Howard also urged MPs to back Mr Johnson’s deal and warned against the economic impact of further uncertainty.
Lord Howard of Lympne told the first Lords Saturday sitting since 1982 that the result of the 2016 EU referendum must be respected and implemented.
“I congratulate the Prime Minister on the result of his negotiations,” he said. “He has achieved what I believe is a good deal – a deal many thought was impossible and I believe he deserves full credit for that.”
Lord Howard said forecasts for the economic damage Brexit could cause may well prove mistaken, and warned any rejection of the deal would just cause more uncertainty.
The UK’s economic performance had been “held back” by uncertainty over the last three years and an extension, or a further referendum or a general election would increase the uncertainty.
He said: “This deal presents a unique opportunity to resolve this most intractable issue and to move on and bring our country together again.”
Before the government’s defeat over the Letwin amendment, the Prime Minister himself warned any further delay would be “pointless” and “corrosive” of public trust ahead of the votes on Saturday.
With Parliament sitting on Saturday for the first time in 37 years, the Prime Minister said the agreement he struck in Brussels represented “the best possible solution”.