Additional district and sessions judge found Binay Sah guilty of murdering Amrita Devi, an anganwadi worker, with a sharp weapon over personal enmity at Simri village of Darbhanga district in April 2010.
The court also slapped a fine of Rs 30,000 on him.
According to the prosecution, Sah had also tried to kill Amrita Devi's husband and daughter.