Greg Brown III was born on December 1, 2001. Athletes run in his family as his father played football for the Denver Broncos and his uncle played professional basketball overseas. Hailing from Austin, Texas, Brown rose to prominence at Vandegrift High School as a four-year starter on varsity and was a five-star recruit. In the spring of 2020, Brown committed to the University of Texas, over Auburn, Memphis, Michigan, Kentucky, and an offer from the G League. In his one season with the Longhorns, Greg was an All-Big 12 honorable mention and an All-Freshman and All-Newcomer Team selection.