In return, he will cooperate with Special Counsel Robert Mueller and his team.
In a statement, the White House distanced Mr 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.
In the past year, Mueller has secured pleas from a former national security adviser who lied to the Federal Bureau of Investigation about discussing sanctions with a Russian ambassador, a campaign aide who broached the idea of a meeting with Russian President Vladimir Putin; and another aide who was indicted alongside Manafort but ultimately turned on him.
Image copyright Reuters Image caption Paul Manafort seated (L) as his lawyer speaks in court. They were all hugging and congratulating each other at the end of the hearing. The reason: "the President did nothing wrong", said Giuliani. "I'm confident", he replied, without saying whether Manafort's lawyers had given him this assurance.
Manafort, 69, also pleaded guilty to two criminal counts on Friday (local time), becoming the most prominent former Trump campaign official to plead guilty in Mr Mueller's investigation.
The Virginia case was the first brought by Mueller to go to trial, and the guilty finding by the jury - on eight of 18 charges - was a significant victory for Mueller's team.
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. And the judge may decide to run those sentences consecutively or concurrently. He appears to admit to the allegations he faced in both Virginia federal court and DC district court, describing his use of offshore bank accounts to move the money, deceive his accountants and bookkeeper and then spend the money on lavish purchases and real estate. But that is more than the statutory maximum which is five years, which the judge can not exceed.
The information says Manafort conspired to act as an unregistered agent for the government of Ukraine and its former pro-Russian president, Victor Yanukovych, generating more than $60 million in income.
Manafort entered his plea in the U.S. District Court in Washington, D.C. on September 14, just days before his second federal trial was scheduled to begin.
Over the past several months, Manafort's legal options slimmed as the special counsel notched several wins against him, including sending him to jail, securing several cooperators and gaining convictions. He shook his head and said "no".
"In other words: "'If you don't think we're doing something important, read this, '" he said of the filing.
Manafort's attorney Kevin Downing said Manafort "wanted to make sure that his family was able to remain safe and live a good life".
"Now, he's doing the thing that will keep Trump from giving him a pardon: He's giving up everything he knows about Trump", Litman said.
The charges in the information say that Manafort will have to forfeit property that was derived from or traceable to his offenses.
The structure of Manafort's plea deal limits the effectiveness of any Trump pardon, said Jed Shugerman, a law professor at Fordham University.
The scope of the cooperation was not immediately clear.