The jury, after almost four days of deliberations, found Manafort guilty of two of nine bank fraud charges, all five tax fraud charges he faced and one of four charges of failing to disclose foreign bank accounts.
Judge T.S. Ellis declared a mistrial on 10 of the 18 counts, after the jury told him it could not reach a verdict on those charges.
The trial of Manafort, a veteran Republican operative, is the first stemming from Special Counsel Robert Mueller's investigation of Russia's role in the 2016 US election. The charges against Manafort largely predate his work on President Donald Trump's successful campaign.
Prosecutors accused Manafort, 69, of hiding from US tax authorities $16 million he earned as a political consultant for pro-Russian politicians in Ukraine to fund an opulent lifestyle and then lying to banks to secure $20 million in loans after his Ukrainian income dried up and he needed cash.
The verdicts completed a stunning fall for Manafort, a once-powerful political fixer and consultant and well-known figure in Republican politics for decades.
Meanwhile, Trump's former personal lawyer, Michael Cohen, has pleaded guilty to campaign finance violations and other charges, saying he made payments to influence the 2016 election at the direction of a candidate for federal office.
Cohen, 51, appearing in federal court in Manhattan, pleaded guilty to one count of willfully causing an unlawful corporate campaign contribution and one count of making an excessive campaign contribution.
He said he arranged to make payments "for (the) principal purpose of influencing (the) election" at the direction of a candidate for federal office but did not give the candidate's name.
Cohen, who agreed to a plea bargain with federal prosecutors earlier in the day, also pleaded guilty to five counts of tax fraud and one count of making false statements to a financial institution.
His voice cracked as he answered questions from Judge William Pauley III.
Federal prosecutors in New York began investigating Cohen after a referral from US Special Counsel Robert Mueller, who has been investigating Russian meddling in the 2016 election and possible coordination with the Trump campaign.