Garnett played three seasons of high school basketball in South Carolina before transferring to a school in Chicago for his senior year. In 1995 the 6-foot 11-inch (2.1-metre) Garnett averaged 25.2 points, 17.9 rebounds, 6.7 assists, and 6.5 blocked shots per game while leading his team to a city championship, and he was named national Player of the Year by numerous organizations. After earning the Most Valuable Player award at the McDonald's All-American basketball game and providing an impressive workout for National Basketball Association (NBA) scouts, he declared himself eligible for the 1995 NBA draft. He was chosen by the Minnesota Timberwolves as the draft's fifth overall selection, becoming the first person in 20 years to be drafted by an NBA team directly from high school.

Garnett made an immediate impact on the NBA; his mix of size, athleticism, and shooting ability made him a difficult matchup for his opponents. In his second season, he was chosen to play in the NBA All-Star Game, and he led the Timberwolves to the franchise's first play-off appearance. In 1997 he signed a contract extension that promised him $126 million over six years—the highest-paying long-term contract in the history of American professional sports at that time. Garnett's stint in Minnesota produced a string of notable individual accomplishments—he was named an All-Star in 10 of his first 12 seasons and was the NBA's Most Valuable Player for the 2003–04 season—but his team advanced past the first round of the play-offs only once and never made it to the NBA finals. After the 2006–07 season, the Timberwolves' management decided to enter into a rebuilding period, and they traded Garnett to the Boston Celtics for a record seven players. In his first year with Boston, he was named NBA Defensive Player of the Year, and he teamed with fellow All-Stars Ray Allen and Paul Pierce to lead the Celtics to the NBA championship.