The MP/MLA court in Ghazipur on Thursday convicted and sentenced Mukhtar Ansari to ten-year imprisonment in a 1996 case under the Gangsters Act.
His aide Bhim Singh has also been awarded a ten-year sentence by the court.
The court has also imposed a fine of Rs five lakh each on the two.
This is the first case in which Ansari has been convicted by the court. It relates to the murder of Avadesh Rai, brother of Congress zonal president Ajai Rai, in 1996.
Rai had testified in court against Mukhtar Ansari.
Ansari has been lodged in various jails since 2005, but managed to get acquitted in most other cases.