Gates testified against Manafort in the Virginia trial, saying his former boss had directed him to commit the fraud.
The move allows Manafort to avoid a second criminal trial and ends his more than year-long fight against investigators in the Russian Federation probe.
As part of the run-up to the second trial, Manafort's lawyers filed hundreds of pages in court to fight prosecutors' allegations - having brought two appeals unsuccessfully - and his legal fees mounted to more than $1 million, according to two people familiar with his case.
Sandick said one reason Mueller's team might want to do so is "in part a response to criticism of the investigation".
Manafort already faces an eight to 10 year sentence after the jury in a separate Virginia trial convicted him on August 21 of eight counts of financial wrongdoing. Mueller has also gotten guilty pleas from former national security adviser Michael Flynn and former foreign policy adviser George Papadopoulos, while Trump's longtime personal attorney Michael Cohen pleaded guilty in a case referred to the Southern District of NY by Mueller's office.
He smiled broadly as he entered the courtroom Friday but gave terse and barely audible answers during questioning from the judge.
"This had absolutely nothing to do with the President or his victorious 2016 Presidential campaign", she said. "It is totally unrelated".
In a court document, Manafort said he was guilty of plotting against the United States and plotting to obstruct justice.
The plea deal allows Manafort to avoid a second trial scheduled to begin next week in Washington. Separately, Trump's former personal attorney, Michael Cohen, implicated him in a criminal campaign finance violation during his own plea hearing in federal court last month. Manafort's attorneys had argued that the trial should be moved to Roanoke, Virginia, because the intensity of publicity in Washington made it impossible for him to receive a fair trial. He did not elaborate on the agreement. Yet, Jackson said the request appeared to relate more to concerns about the political affiliation of Washington residents, rather than a unique amount of pretrial publicity. In this scenario, Manafort, in vowing to cooperate with the prosecution, would be seeking to force Trump's hand on the issue of a pardon. Manafort is now only facing charges of conspiracy against the United States and conspiracy to obstruct justice.
That posture drew plaudits from Trump, who praised his former campaign chairman for his unwillingness to cooperate with the special counsel.
Manafort, in a trial set to begin September 24 in federal court in Washington, is facing seven counts of foreign lobbying violations and witness tampering.
But given Manafort's pre-existing financial connections to Russia, his agreement to help prosecutors with further investigations will most certainly feed speculation and theories that there's more to these relationships than we're now publicly aware of, beyond what we've been told about Russian lobbyists offering stolen emails and data from Hillary Clinton's campaign to Trump's team. "It shows you've admitted your guilt", he said on Friday before a deal was announced. The network cited three unidentified sources with knowledge of the deal.
For example, the government did not specify how much of a reduction it will seek on Manafort's sentencing if he follows through on his cooperation agreement.