Lewis starred at Bishop O'Connell High School in Arlington, Virginia and chose James Madison University (JMU) for college.

He entered the starting lineup for the Dukes, averaging 14.5 points and 3.5 rebounds per game in his freshman season, earning Colonial Athletic Association (CAA) All-Rookie Team honors.

In his junior year, Lewis again improved his scoring average to 19 points per game and earned second-team All-CAA honors, though the Dukes experienced little on-court success, finishing in last place.

After head coach Louis Rowe was fired, Lewis chose to declare for the 2020 NBA draft, though he retained his college eligibility by not hiring an agent.

Lewis was named the national player of the week by the United States Basketball Writers Association on January 17, 2021, after hitting a school record nine three-pointers in a 30-point effort against Towson.