At Trinity High School in Euless, Texas, Turner was a regular scorer while consistently dominating defensively with rebounds and blocks, averaging 18.1 points, 12.2 rebounds, 3.5 assists, and 6.8 blocks per game in his high school career. An ankle injury on the AAU circuit before his junior year looked to have damaged his recruitment chances, but his standout play as a high school senior brought him national recruiting attention regardless. ESPN ranked him the second-best prospect in his class and the top prospect in the state of Texas. Turner, from Bedford, Texas, chose to commit to college basketball with the University of Texas Longhorns.

In addition to playing for Trinity High, Turner attended many top camps, played in the 2014 McDonald’s All-American Game, and helped the United States claim a gold medal in the 2014 FIBA U-18 tournament.

Turner had a strong 2014-2015 season with the University of Texas Longhorns, winning Big 12 Freshman of the Year honors. In 34 games he had season stats of 10.1 points, 6.5 rebounds, and 2.6 blocks per game. The team finished with a 20-14 record and a first-round exit in the NCAA tournament.

Following his single season at Texas, Turner declared for the 2015 NBA draft.

Turner was selected 11th overall by the Indiana Pacers in the 2015 NBA draft. He missed about a quarter of the season due to thumb surgery, but came back from injury and had several games where he displayed his potential, including a 31-point performance against the Golden State Warriors. The team earned the seventh seed in the playoffs, and Turner was named to the All-Rookie Second Team.

Turner’s sophomore season is his highest-scoring regular season to date, averaging 14.8 points per game. His three-point shooting developed to reach 35% on 1.4 attempts per game, while he also posted his best season rebounding mark to date, at 7.3 per game.

2017-2018 saw a major reshuffle of the Pacers’ lineup, with Paul George departing and Victor Oladipo and Domantas Sabonis entering from OKC. Turner continued his development despite sharing minutes with Sabonis and missing some games through injury. The season ended with a tight seven-game playoff series loss to the Cleveland Cavaliers. Turner’s growth was rewarded with a $72 million dollar contract extension signed in the summer of 2018. In 2018-2019, Turner logged career highs in single-game rebounds (17) and blocks (7). He finished the season as the league leader in blocks and generated some Defensive Player of the Year buzz.

Prior to the 2020 suspension of the season due to coronavirus, Turner and Sabonis had started the majority of Indiana’s games together, forming a formidable frontcourt that anchored the team despite Victor Oladipo missing much of the season to injury.