Judge A Mohamed Jiyautheen sentenced Manikandan to undergo separately the two life terms and the 10-years rigorous imprisonment.
The separate jail terms awarded to a convict for different offences generally run concurrently, but in this case all the three jail terms would run one after another, said a legal expert.
The prosecution case was that 26-year-old Manikandan had murdered his cousin P Revathi following a dispute over money and killed her son Vignesh, who was a witness to the crime.