Garnett was born in Greenville, South Carolina on May 19, 1976, to Shirley Garnett and O'Lewis McCullough, the second of his mother's three children. After divorcing McCullough, Shirley Garnett raised Kevin and his two siblings. She then re-married and moved the family to Mauldin, South Carolina when Kevin Garnett was twelve.
 
Garnett fell in love with the sport of basketball while attending Hillcrest Middle School, although he did not play organized ball until high school. In his first three high school years, Garnett played for Mauldin High School. However, during the summer prior to his senior year of high school, Garnett was in the general vicinity of a fight between black and white students. Although not directly involved, Garnett was one of three students arrested for second-degree lynching, a charge he managed to expunge through a pre-trial intervention. Due to the racially charged incident and fearful of being a target, Garnett decided to leave Mauldin. He transferred to Farragut Career Academy in Chicago, Illinois for his senior year of high school. He led Farragut to a 28–2 record and was named National High School Player of the Year by USA Today. He was named Mr. Basketball for the State of Illinois after averaging 25.2 points, 17.9 rebounds, 6.7 assists and 6.5 blocks while shooting 66.8% from the field. In four years of high school, Garnett posted an impressive 2,553 points, 1,809 rebounds and 737 blocked shots. He was named the Most Outstanding Player at the McDonald's All-American Game after registering 18 points, 11 rebounds, 4 assists and 3 blocked shots, and then declared himself eligible for the 1995 NBA Draft. In high school, Garnett played alongside Ronnie Fields, who also became a professional basketball player. To mark the 35th anniversary of the McDonald’s All American High School Boys Basketball Game, Garnett was honored as one of 35 Greatest McDonald's All Americans.