The court in New York City convicted Mehmet Hakan Atilla on five counts of conspiracy, including conspiracy to defraud the United States, plus one count of bank fraud.
Prosecutors have also charged Turkish-Iranian business tycoon Reza Zarrab and his co-conspirators of handling hundreds of millions of USA dollars for Iran's government and Iranian entities from 2010 to 2015. He was acquitted of a money laundering charge.
Jurors returned their verdict on the first day following a holiday break after having failed to reach a verdict during three days of deliberation in December.
However, last March, when Zarrab inexplicably brought his family to America for a vacation at Disney World, U.S. authorities arrested him in Florida for engaging in conspiracies to violate sanctions, commit bank fraud, and launder money.
"I am saddened to say this, but this is how it will be from now on", Erdogan told a news conference before his departure to France for an official visit.
"If this is the U.S. understanding of justice then the world is doomed".
Zarrab testified that from 2012 to 2015, he made profits of $100 to $150 million from the scheme.
Boente and Acting U.S. Attorney Joon H. Kim for the Southern District of NY made the announcement.
Zarrab alleged top Turkish officials, including Erdogan, personally authorised two Turkish banks to join the scheme when he was prime minister, in addition to other ministers. But Zarrab was freed and Korkmaz was jailed along with other police and prosecutors in a subsequent purge, he said.
The case relied in part on documents and wiretaps from a 2013 Turkish corruption probe that were spirited out of the country by a former Istanbul police official, Huseyin Korkmaz, who also testified in the NY trial.
Prosecutors said Atilla was a critical part of the plot - a sanctions expert at Halkbank, who helped bank officials who were taking bribes and Zarrab fend off questions from the United States.
Atilla was accused of orchestrating a complex Iranian oil for gold scheme.
Sentencing is scheduled for April 11.
He also cited meetings and phone calls as proof Atilla was intimately involved in the investigation, but the defense was able to show Atilla was on a plane with no cellphone service at the time of one of the calls.
Atilla, Zarrab and others used deceptive measures to provide access to worldwide financial networks, including USA financial institutions, to the Government of Iran, Iranian entities and entities identified by the Department of the Treasury Office of Foreign Assets Control as Specially Designated Nationals (SDNs).