A justice official announced the punishment today, noting that Zanjani, who became notorious for finding ways to channel hard currency from oil sales during the sanctions-ridden era of president Mahmoud Ahmadinejad from 2005 to 2013, could appeal.
Zanjani rose to prominence after sanctions imposed on the Islamic republic's banks as punishment for its nuclear programme hit the country's finances hard.
Having taken commissions, he said he was at all times working with the knowledge and backing of Ahmadinejad's government and he boasted in media interviews of his skills and wealth amassed by managing to subvert the banking restrictions.
But he was arrested in December 2013, three months after current President Hassan Rouhani took office, having pledged to crack down on corruption.
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Zanjani, 41, was convicted of fraud and economic crimes and must repay money to the state as well as face the death penalty, judiciary spokesman Gholam Hossein Mohseni-Ejeie said.
The trial was public, a rarity for such a major case in Iran, and two other accused were also convicted of "corruption on earth", the most serious offence in the Islamic republic, meaning they too will face the death penalty.
They must also pay a "fine equal to one fourth of the money that was laundered", the spokesman said, without specifying the sum.
Zanjani had denied wrongdoing, insisting the only reason the money had not been paid to the oil ministry was that sanctions had prevented a planned transfer from taking place. That claim was disputed in court.
The case follows repeated declarations from Rouhani's government that corruption and the payment of illegal commissions thrived under Ahmadinejad's rule. Other trials are ongoing.