Mr. Atilla, the deputy general manager for international banking at Halkbank, a Turkish state bank, was the only defendant to be tried. A co-defendant, Reza Zarrab, a wealthy gold trader, pleaded guilty shortly before the trial began and became the star prosecution witness. The seven other defendants are still at large.

Mr. Atilla, 47, was described by prosecutors as a “fixer” who helped Iran circumvent the sanctions and gain access to billions of dollars of restricted petrodollar funds that were being held at the bank.

In testimony over seven days, Mr. Zarrab described an illicit operation that relied on false documents and front companies. He also described support from the highest levels of the Turkish government, as well as from Iranian officials and Halkbank, an institution that prosecutors said was critical to the scheme’s success.

Mr. Zarrab testified that in 2012, Mr. Erdogan, then Turkey’s prime minister, ordered that two Turkish banks be allowed to participate in the sanctions evasion scheme. He also told the jury that he had paid tens of millions of dollars in bribes to Zafer Caglayan, then Turkey’s economy minister, and additional bribes to Suleyman Aslan, the general manager of Halkbank, for help in facilitating the operation. Mr. Caglayan and Mr. Aslan are among the defendants still at large in the case.

Mr. Zarrab, 34, testified that he had made as much as $150 million from the scheme.

Prosecutors portrayed Mr. Atilla as a sanctions expert who designed the complex scheme and then lied to United States Treasury Department officials about it. He lied again, they argued, when he testified in his own defense at the trial.