Shahabuddin has been languishing in jail for several years in connection with several serious criminal cases.
The special court in Siwan district found Shahabuddin guilty in a 2004 case in which he and his men were charged with giving an acid bath to two brothers Girish Raj and Satish Raj and murdering them.
The court will pronounce sentencing on December 11.
Shahabuddin has been convicted on charges of criminal conspiracy, kidnapping and murder.
Shahabuddin's son Osama has also been charged with killing of a local BJP leader Rajiv Roshan, who was a witness in the murder case of the two brothers in which Shahabuddin has been convicted.
The two brothers were kidnapped allegedly at Shahabuddin's behest and drenched in acid before being murdered.