Kayleigh Haywood, from Measham, Leicestershire, was killed and her body was dumped in a hedgerow in November 2015 after being groomed online.
Stephen Beadman, 34, was given a life sentence with a minimum term of 35 years in 2016.
The Prison Service said he died at HMP Wakefield and the Prisons and Probation Ombudsman had been informed.
Kayleigh Haywood’s disappearance sparked a large scale five-day search resulting in her body being discovered
A spokesperson said: “The Prison Service cannot confirm the cause of death, which is rightly a matter for the coroner.”
Beadman, who had admitted murdering and raping Kayleigh, was also convicted at Nottingham Crown Court of falsely imprisoning her.
The court heard she had agreed to stay at a flat in the village of Ibstock after being groomed online, but was seen running away in the early hours of 15 November.
Beadman chased, raped and then beat her to death.
Kayleigh had been chatting with a friend of Beadman’s, Luke Harlow, on social media just two weeks before she was killed.
They exchanged hundreds of text messages and it was in his flat that she was attacked.
Harlow was jailed for 12 years for sexually touching and falsely imprisoning Kayleigh, and grooming her and two other girls.
It has not yet been revealed how Beadman died.