Juan Thornhill was born October 19, 1995, in AltaVista, Virginia. He played safety and quarterback at AltaVista High School, where he helped the team win back to back state championships. He also played basketball, and they won three state championships. He chose to play college for the University of Virginia, where he graduated with a degree in Anthropology in December 2018.
He was drafted by the Chiefs in the 2nd round of the 2019 draft and became the 16th player in team history to start all 16 games of his rookie season.