It is now unclear what Manafort has offered the special counsel in return for the lighter charge sheet, but multiple news outlets have speculated that it could be damaging information on Trump and alleged Russian interference in the 2016 presidential election.
The White House distanced Trump from the man who helped get him elected in November 2016 against the odds in a bitterly contested campaign in which he defeated Democrat Hillary Clinton.
Manafort made a similar unsuccessful request in his bank fraud and tax evasion trial in northern Virginia.
But Manafort's shocking reversal Friday morning indicates how Mueller's team is working behind the scenes, systematically going after lower-level associates and crimes related to finances and false statements, methodically flipping one witness after another. Trump has not said whether he would pardon Manafort, but the president has not publicly ruled it out.
Paul Manafort (centre) is heckled as he walks into court.
"He has accepted responsibility", Manafort attorney Kevin Downing told reporters outside of D.C. District Court after the plea hearing.
On Twitter on August 22, Trump wrote: "Unlike Michael Cohen, he refused to "break" - make up stories in order to get a 'deal".
Manafort, wearing a dark suit, white shirt and purple tie, appeared upbeat as he arrived in court where he quickly took his place at the podium to enter his plea of guilty to two conspiracy counts, including conspiracy to obstruct justice.
As part of the deal, Mr Manafort, 69, could be required to cooperate with Mueller's probe into Russia's role in the 2016 presidential election and whether Trump's campaign colluded with Moscow. In that case, he was found guilty on eight counts of bank fraud, tax fraud and failure to report a foreign bank account.
Manafort has not yet been sentenced in the Virginia case. It has not been established that Trump himself knew about this meeting at the time, but Manafort might be able to testify to that as well.
The charges against Manafort are related to his Ukrainian consulting work - not Russian interference in the 2016 presidential election, which is the central issue in the special counsel's investigation. The president agreed to wait at least until the investigation concludes, Giuliani has said.
Earlier this year, Manafort derided Gates, his former business partner, for striking a deal with prosecutors that provided him leniency in exchange for testimony against his former partner.
Thirteen Russians and three Russian entities were indicted in Mueller's investigation in February, accused of tampering in the 2016 election to support Trump.