Zanjani became notorious during the era of president Mahmoud Ahmadinejad, finding ways to channel hard currency from oil sales to Tehran despite financial sanctions imposed on the Islamic republic's banks as punishment for its nuclear programme.
The 41-year-old was convicted of fraud and economic crimes and as well as facing the death penalty he must repay money to the state, judiciary spokesman Gholam Hossein Mohseni-Ejeie said at his weekly press conference.
"The preliminary court has sentenced these three defendants to be executed, as well as paying restitution to the plaintiff," Mohseni-Ejeie said, adding that that was the oil ministry.
They must also pay a "fine equal to one fourth of the money that was laundered", the spokesman said, without specifying the sum.
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Zanjani, who can appeal, had denied any wrongdoing, insisting that the only reason the money had not been paid to the oil ministry was that sanctions had prevented a planned transfer from taking place.
Zanjani had repeatedly said in media interviews that in return for commissions paid by Ahmadinejad's government he was tasked with circumventing sanctions to get money back to Iran.
In October last year, however, Rouhani's oil minister Bijan Zanganeh signalled the shifting political balance in Iran, hitting out at the use of middlemen such as Zanjani, who before being arrested had boasted of his personal wealth.
Iranian media have put it as high as USD 13.5 billion.