Roundtree was born in Lake City, South Carolina, the youngest in a family of six. His eldest brother Dannie played the trombone for a marching band at the funeral for local astronaut Ronald E. McNair who was killed in the Challenger disaster. Roundtree decided to join the Marines in his sophomore year of High School in 1995. He attended the U.S. Naval Academy and graduated at the rank of Second Lieutenant in 2001.