Gates was expected to be a star witness in the government's case against Manafort having pleaded guilty in February and agreed to co-operate with prosecutors under a deal that could lead to a reduced sentence. His case is the first to go to trial arising from Special Counsel Robert Mueller's investigation into Russian interference in the 2016 US election.
Gates, 46, is already facing up to five years in prison under the terms of a plea deal he struck with prosecutors in February when he pleaded guilty to two charges of conspiracy and lying to the Federal Bureau of Investigation.
When he finished speaking Monday, he had described his history of work with Manafort, his plea deal with prosecutors and how Manafort's consulting operation in Ukraine functioned.
Mr Manafort, 69, could spend the rest of his life in prison if found guilty of all the fraud charges.
Gates said that the foreign accounts were used to receive income they made from their work as political operatives in Ukraine.
Manafort's attorneys have signaled they will seek to blame Gates and have accused him of embezzling millions of dollars from Manafort. Among the tax charges Manafort is facing in Virginia is failure to report the foreign bank accounts.
Gates testified that Manafort told him to report overseas income as loans to lower Manafort's taxable income, supporting the testimony of his accountant. Gates pleaded guilty to financial fraud and to lying to investigators as he negotiated a plea agreement, something defense lawyers will no doubt seize on to try to undercut his credibility.
In early July, Trump's lawyer Rudy Giuliani also suggested Cohen might flip: "If he believes it's in his best interest to cooperate, God bless him, he should cooperate", Giuliani said at the time.
Disappointing: Google Makes Plan To Return To China With Censored Search Engine
It's unclear if Google will get the green light from Chinese officials with the escalating trade dispute with the U.S. Blacklisted information will automatically be removed before the user is served up the results of their search.
All told, prosecutors allege that Manafort failed to report a "significant percentage" of the more than $60 million they say he received from Ukrainian oligarchs. During that part of Gates' testimony, he said that he lied in a deposition - part of an unrelated case - about the private equity firm run by Manafort's consulting group.
Manafort, a flamboyant figure in Washington for decades, became known for his consulting and lobbying work for ethically questionable global leaders like Ukraine's Viktor Yanukovych.
Rick Gates testified today that he committed crimes while working with Paul Manafort.
Judge T.S. Ellis has urged - harshly, at times, including on Monday - for the prosecutors to move their case along more quickly.
The President is watching proceedings carefully as Mueller appears to be moving closer to his inner circle on multiple fronts and has complained that Manafort has been treated like a mobster - even as the White House has tried to open up some distance between Trump and his former campaign chairman.
But Laporta's testimony raised the stakes for Manafort, legal experts said.
Gates came out swinging from the witness box. The defense introduced its own documents to the jury for the first time - rather than relying on the prosecutors' binders of evidence - and showed that Manafort had paid $8 million in taxes over 10 years. Mueller is also investigating possible coordination between Trump campaign members and Russian officials in the election campaign, but the charges against Manafort do not address that.
Downing also accused Gates of embezzling "millions", a higher amount than Gates later admitted to in his testimony.
Later, they say, when that income dwindled, Manafort launched a different scheme, shoring up his struggling finances by using doctored documents to obtain millions more in bank loans.