The deal gives special counsel Robert Mueller a key co-operator who steered the Trump election effort for a pivotal stretch of the 2016 presidential campaign. The result also ensures the investigation will extend far beyond the November congressional elections despite entreaties from the president's lawyers that Mueller bring it to a close.

It is unclear what information Manafort is prepared to offer investigators about the president or that could aid Mueller's investigation into Russian interference in the 2016 election. But his involvement in key episodes under scrutiny, and his leadership of the campaign at a time when prosecutors say Russian intelligence was working to sway the election, may make him an especially valuable witness.

The agreement makes Manafort the latest associate of Trump, a president known to place a premium on loyalty among subordinates, to admit guilt and work with investigators in hopes of leniency.

Mueller has already secured cooperation from a former national security adviser who lied to the FBI 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. Trump's former personal lawyer has separately pleaded guilty in New York.

Friday's deal, to charges in Washington tied to Ukrainian political consulting work but unrelated to the campaign, was struck just days before Manafort was to stand trial for a second time.

He was convicted last month of eight financial crimes in a separate trial in Virginia and faces seven to 10 years in prison in that case. The two conspiracy counts he admitted to on Friday carry up to five years, though Manafort's sentence will ultimately depend on his cooperation.

The agreement doesn't specify what if anything prosecutors hope to receive about Trump, but Manafort could be well-positioned to provide key insight for investigators working to establish whether the campaign coordinated with Russia.

He was among the participants, for instance, in a June 2016 Trump Tower meeting with Russians and Trump's oldest son and son-in-law that was arranged for the campaign to receive derogatory information about Democrat Hillary Clinton.

Under the terms of the deal, Manafort was allowed to plead guilty to just two counts, though the crimes he admitted largely cover the same conduct alleged in an indictment last year. He abandoned his right to appeal his conviction in Virginia and agreed to forfeit homes in New York, including a condo in Trump Tower.

But the guilty plea also spares Manafort the cost of a weeks-long trial that could have added years to the prison time he's already facing following the Virginia guilty verdicts. A jury there found him guilty of tax evasion, failing to report foreign bank accounts and bank fraud. Jurors deadlocked on 10 other counts.

Australian Associated Press