The deal for 21-year-old Harris runs through the 2030 season and includes team options for 2031 ($15 million) and 2032 ($20M).
Harris was the team's top prospect entering the season, leading to a major league call-up in late May. The youngest player in the majors hasn't missed a beat since, hitting .287 with 12 home runs, 13 steals and 39 RBI in 71 games.
He was named NL Rookie of the Month in June, currently leads all qualified rookies with an .825 OPS and has played strong defense in the outfield for reigning World Series champs.
Atlanta has made a habit of locking up its young talent in recent seasons. The team signed star third baseman Austin Riley to a 10-year, $212 million extension earlier this month, and now has Harris, Riley, Ronald Acuna Jr. and Ozzie Albies all signed through at least 2025.
All four players are ages 25 or younger.
In addition, first baseman Matt Olson, 28, is signed through the 2029 season (with a club option for 2030).