R.J. Nembhard was born in Kessler, Texas, in March of 1999. He is the son of Ruben and Terri Nembhard, and his father played one season in the NBA while his sister Jayden plays volleyball at Kansas St. Nembhard was a four-star recruit in the 2017 class and committed to TCU after a standout high school career in which he averaged 25.7 points and 6.7 rebounds per game his senior season. He played four seasons for the Horned Frogs, redshirting his freshman season after only playing six games. He evolved into a full-time starter his last two seasons, averaging 15.7 points on 40 percent shooting his junior season to earn third-team All-Big 12 honors. Nembhard ultimately decided to forgo his senior season and enter the 2021 NBA Draft, in which he would go undrafted. Following the draft, Nembhard was on the Miami Heat's Summer League team and eventually signed a two-way contract with the Cleveland Cavaliers and their G-League affiliate.