Tong Sang and two of his former ministers, Clarenntz Vernaudon and Fernand Roomataaroa, were convicted for signing contracts to seal a coalition deal with the Ai'a Api Party.
Tong Sang was fined $US18000.
The three have also been sentenced to jointly pay $US80000 to the public purse.
Their deal in 2008 was allegedly struck to firm up the government coalition.
It involved giving Roomataaroa the agriculture ministry and moving the incumbent into another job as well as upgrading the contracts of 20 of her staff.