Prosecutors filed new charging documents against Manafort which contained a criminal information, a document that can only be filed with a defendant's consent and typically signals a deal has been reached.
The details of Manafort's plea were not immediately clear, including whether he would be providing any information to special counsel Robert Mueller as part of any deal.
Former Trump campaign manager Paul Manafort arrives for arraignment on a third superseding indictment against him by Special Counsel Robert Mueller on charges of witness tampering, at U.S. District Court in Washington, U.S. June 15, 2018.
"If he's helping out Mueller, that's more bad news for Trump".
The charges do not relate to Russian interference in the 2016 presidential election, and jurors are expected to only hear limited references to Manafort's role in the campaign.
Another approach would be for Manafort to plead guilty without cooperating in hopes of a presidential pardon.
Paul Manafort will plead guilty to avoid a second trial. Had that juror been persuaded on the ten mistrial charges, Manafort could have been convicted of 18 criminal counts in Alexandria instead of "only" eight.
The plea deal is expected to be announced Friday morning, when Manafort is due in court. He left the campaign in August that year - days after the New York Times reported a Ukraine investigation had uncovered $12.7 million in undisclosed cash payments involving Manafort from 2007 to 2012.
Manafort's legal team blamed most of his problems on former business partner Rick Gates, who pleaded guilty this year and testified against Manafort in Virginia.
Moscow has denied interfering in the 2016 election and Trump has said there was no collusion.
The decision by Trump's onetime personal lawyer, Michael Cohen, to plead guilty last month in a federal investigation in Manhattan particularly angered the president, who denounced him as a "flipper".
Writing on Twitter on August 22, Mr. Trump said, "Unlike Michael Cohen, he refused to "break" - make up stories in order to get a 'deal.' Such respect for a fearless man!"