There was some concern about the risk to Mr Mueller's investigation faced going into the Manafort trials. Usually it helps you get a pardon down the road.
He led the campaign in mid-2016 when Trump was selected as the Republican presidential nominee at the party convention.
If he cooperates, Mueller could be a significant witness for prosecutors in the case.
As recently as last month, Trump praised his former campaign manager, who he said said was a "brave man" who "refused to break".More news: Hurricane Florence: Giant, slow-moving storm causes deluge as it makes landfall
The high-profile lobbyist is expected to appear in court later Friday morning at 11 a.m. EST.
On another conspiracy-related front, as Natasha Bertrand points out today, Manafort might be in a good position to shed light on what exactly former Trump campaign aide George Papadopoulos - who has testified as part of his own plea deal that he learned that Russian Federation had stolen dirt on Clinton in the form of "thousands of emails" - might have told campaign higher ups about this at the time, another big unknown. Any deal would not be final until Manafort admits guilt before the judge, who would need to approve the plea. A jury there convicted him on eight counts of filing false tax returns, failing to report foreign bank accounts, and bank fraud.
In addition to being the first conviction won by Mueller, Manafort is the fifth person to plead guilty to charges stemming from Mueller's investigation.
In addition to the criminal charges, prosecutors said in a court filing that Manafort could be forced to forfeit assets that would deal him a significant financial blow: four houses he owns, including an expansive retreat in the Hamptons, plus four bank accounts and the proceeds of a life insurance policy.
The punishment that Manafort may receive related to his D.C. case, and any cooperation he may have offered the government, weren't immediately clear.More news: Meghan Markle Reportedly Losing Friends Since Joining The Royal Family
Manafort pleaded guilty to one count of conspiracy against the USA and one count of conspiracy to obstruct justice due to attempts to tamper with witnesses, according to a court filing Friday.
And during his Virginia trial in August, Manafort's lawyers spent considerable time painting Mr Gates as a liar, embezzler, philanderer and turncoat who would say anything to get a lighter prison sentence.
It's true that nothing public in Mueller's investigation so far has touched Trump on the central questions of collusion with Russian Federation or obstruction of justice. Trump's critics have pointed to the meeting as evidence of the collusion with Russian Federation that Trump denies.
The charges do not relate to Russian interference in the 2016 presidential election. He had been jailed since June as a result of the witness tampering charges.
"He knows nothing harmful to the president and the plea is the best evidence of that", Rudy Giuliani, the former New York City mayor who is representing Trump in the Russian Federation probe, told Reuters.More news: Ariana Grande Remembers Mac Miller with Heartfelt Tribute