Additional District and Sessions court pronounced the sentence in presence of the accused, who has also been charged for murdering 16 girls and slapped a fine of Rs 25,000 on him.
Mahanand (40), was arrested in 2009 after the victim, his wife's friend, complained to the Ponda police that he was threatening her. The girl had claimed that he was raping her for over three years.
The victim, belonging to a poor family, had said she was being "blackmailed" by Mahanand by showing her semi nude pictures.
During interrogation after his arrest, Mahanand had confessed of killing 16 women for over 15 years.
The killer had confessed that he was murdering the girls using their dupatta after luring them for a date.