Additional Sessions Judge Sanjay Kumar sentenced Pappu, his father Ram Baran and mother Sita Devi to life imprisonment after finding them guilty of murdering Laxmi in Gangadeen Purwa village in April 2012.
The court also imposed a cash fine of Rs 5,000 each on the accused.
According to prosecution, Laxmi's father Triloki Nath Jaiswal had lodged an FIR accusing the three of murdering his daughter.