“When the rubber hit the road,” Mr. Lockard said, “Mr. Atilla chose lies and deceptions, not honesty and integrity.”

Image Mehmet Hakan Atilla, in a photo from social media

“This is not a case about drugs,” Mr. Lockard said. “It’s not a case about shipments of weapons. But it is, in a very real sense, a case about nuclear capability. Nuclear capability by the world’s foremost state sponsor of terrorism."

Judge Berman did not contest the gravity of the sanctions evasion plot. And he noted that Mr. Zarrab had given “credible” and “largely unrefuted” testimony at Mr. Atilla’s trial about how the conspirators had been able to “transfer or free up millions upon millions of dollars of Iranian proceeds, primarily from the sale of Iranian oil,” in violation of the sanctions.

But Judge Berman indicated that Mr. Atilla’s role did not warrant the longer sentence the government was seeking. The judge also noted that Halkbank had not been charged in the case.

Mr. Atilla will be credited with the time he has spent in jail since his March 2017 arrest.

One of Mr. Atilla’s lawyers, Victor J. Rocco, called the sentence fair but said his client would appeal the conviction. “Our objective is to get him home as quick as possible,” Mr. Rocco said.

At Mr. Atilla’s trial late last year, Mr. Zarrab testified that he had paid millions of dollars in bribes to Zafer Caglayan, then Turkey’s economy minister, and Suleyman Aslan, the general manager of Halkbank, to facilitate the scheme. (Mr. Caglayan and Mr. Aslan were among the seven other defendants charged in the case, who all remain at large.) Mr. Zarrab also suggested in his testimony that Recep Tayyip Erdogan, when he was Turkey’s prime minister in 2012, approved the operation.