The merchants had been accused of speculating on food prices when Iraq was subject to UN sanctions after its invasion of Kuwait in 1990.
Al-Majid already has three death sentences against him - the most recent of which was delivered on March 2 - for the murder of Shia Muslims 10 years ago.
Aziz was acquitted of war crimes charges during that court session.
Wednesday's conviction is the first against Aziz, 73, who acted as Saddam's spokesman for two decades.
Badee Arif, Aziz's laywer, promised to appeal saying the case was politicised.
"We were very much sure that Tariq Aziz is to be released, taking the law procedures into considerations," he told Al Jazeera. "But, apparently there's been a political decision made by [the] Iraqi government."
Arif said the government may be trying to use Aziz as a bargaining chip in its push for a national reconciliation agreement.
Al-Majid and Aziz are also among 16 former officials on trial for a violent campaign against Shia Kurds.
They are accused of gassing members of the Fayli Kurdish community as part of a chemical weapons testing programme and as human shields during Iraq's war with neighbouring Iran from 1980 to 1988.
Aziz surrendered to US forces in April 2003 after Saddam Hussein's government was overthrown.