Former Trump campaign chairman Paul Manafort has been found guilty of eight financial crime charges in a US court in the first trial victory for special counsel Robert Mueller’s team.

A judge declared a mistrial on 10 other counts the jury could not agree on.

The verdict was part of a stunning one-two punch of bad news for the White House, coming as the president’s former lawyer, Michael Cohen, was pleading guilty in New York to campaign finance charges arising from hush money payments made to two women who say they had sex with Mr Trump.

The jury returned the decision after deliberating four days on tax and bank fraud charges against Manafort, who led the Mr Trump election effort during a crucial stretch of 2016.

Manafort, who appeared jovial earlier in the day amid signs that the jury was struggling in its deliberations, stared intently at the panel as the clerk read off the charges.

He stared down blankly at the defence table, then looked up, expressionless, as the judge finished thanking the jury.

Manafort was found guilty of five counts of filing false tax returns on tens of millions of dollars in Ukrainian political consulting income.

Paul Manafort booked into the William G. Truesdale Adult Detention Center last month. Photo: AAP

He was also convicted of failing to report a foreign bank account and of two bank fraud charges that accused him of lying to banks to obtain millions of dollars in loans after his income dried up.

The outcome, though not the across-the-board guilty verdicts the prosecutors sought, almost certainly guarantees years of prison for Manafort.

It also appears to vindicate the ability of special counsel Robert Mueller’s team to secure convictions from a jury of average citizens despite months of partisan attacks – including from Mr Trump – on the investigation’s integrity.

The verdict raised immediate questions of whether the president would seek to pardon Manafort, the lone American charged by Mr Mueller to opt for trial instead of cooperate.

The president has not revealed his thinking but spoke sympathetically throughout the trial of his onetime aide, at one point suggesting he had been treated worse than gangster Al Capone.

The trial, presided over by the colourful and impatient US District Judge TS Ellis III, captured Trump’s attention as he sought to undermine Mueller’s investigation through a constant Twitter barrage and increasingly antagonistic statements from his lawyer-spokesman, Rudy Giuliani.

Disgraced and discredited Bob Mueller and his whole group of Angry Democrat Thugs spent over 30 hours with the White House Councel, only with my approval, for purposes of transparency. Anybody needing that much time when they know there is no Russian Collusion is just someone….

— Donald J. Trump (@realDonaldTrump) August 20, 2018

But the Trump campaign comprised but a fraction of the trial as jurors instead heard detailed and sometimes dull testimony about Manafort’s finances and what prosecutors say was a years-long tax-evasion and fraud scheme.

Manafort decided not to put on any witnesses or testify himself. His attorneys said he made the decision because he didn’t believe the government had met its burden of proof.

Manafort’s defence team attempted to make the case about the credibility of longtime Manafort protege Rick Gates, who served as the government’s star witness.

They attacked him as a liar, embezzler and instigator of any crimes as they tried to persuade jurors that Manafort didn’t wilfully violate the law.