Manafort pleaded guilty to one count of conspiracy against the United States and one count of conspiracy to obstruct justice brought by Mr Mueller's team.
Even Harvard University law professor Alan Dershowitz, who has been one of Trump's most staunch defenders in the Russian Federation probe in numerous media appearances, conceded on Friday that Mueller's deal securing Manafort's cooperation was "a big win" and "big get" for the investigation into Trump's ties to Russian Federation, adding, "Potentially it opens up lots of doors that probably haven't been open before", according to an NBC News report.
He also agreed to cooperate fully with the government in criminal investigations and prosecutions, which includes providing documents, testimony, and performing undercover activities.
Manafort joined the Trump campaign in March 2016 and was elevated to chair in May. Five other charges were dropped in the new court filing. "It is totally unrelated".
Manafort will lose several properties, the money in several bank accounts, and a life-insurance policy, which appear to have value well in excess of ten million dollars. The reason: "the President did nothing wrong", said Giuliani.
Former Trump campaign chairman Paul Manafort is expected to plead guilty to federal charges as part of a deal with the special counsel's office.
Read the charges against Manafort.
White House press secretary Sarah Huckabee Sanders released this statement on Manafort.
Gates pleaded guilty in February to helping Manafort use bank accounts in Cyprus and Grenadines to hide millions they had made while lobbying for Ukrainian politicians.
Given his direct involvement in the Trump campaign, including episodes being scrutinized by Mueller, Manafort could be positioned to provide key insight for investigators working to establish whether the campaign coordinated with Russian Federation.
Manafort, who was found guilty last month on eight counts of bank and tax fraud in Virginia, was heading toward a second trial in Washington. He had another trial coming up this month, and this plea deal was his way of avoiding it. But he served as Trump's campaign chairman during the critical summer months 2016, and he attended the now-infamous meeting at Trump Tower that June with a Russian delegation offering dirt on Hillary Clinton.
Still, Friday's move gives Mueller another successful conviction while allowing Manafort to avoid facing another costly public trial.
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.
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.
In 2012, Manafort set out to help his client, Ukrainian President Viktor Yanukovich, by tarnishing the reputation of Yanukovych's political rival, Yulia Tymoshenko, according to the document.
Manafort is still subject to whatever sentence is imposed in the Virginia trial.
Donald Trump Jr, who organised the meeting with Kremlin-linked Russian lawyer Natalia Veselnitskaya and others, initially said it was mainly to discuss a programme on adoptions of Russian children. "Justice" took a 12 year old tax case, among other things, applied tremendous pressure on him and, unlike Michael Cohen, he refused to "break" - make up stories in order to get a 'deal.' Such respect for a fearless man!" With Flynn likely still cooperating, Manafort freshly flipped, Roger Stone in Mueller's sights, and Mueller's reports on conspiracy and potential obstruction of justice incoming, things will only get more interesting from here.