Mahila Court judge Mohammed Jiyauddin sentenced Arunkumar to two life terms and 10 years of rigorous imprisonment.
The sentences will run concurrently, the judge ordered.
The judge also imposed a penalty of Rs 15,000 on the convict and recommended to the Tamil Nadu government to provide an adequate compensation to the family of the victim.
According to the prosecution, Arunkumar had sexually assaulted and murdered the minor girl, a 12th-standard student, when she was alone at her residence in Velliyampalayam in 2013.