Powell attended IMG Academy in Bradenton, Florida. As a senior, he averaged 23.2 points, 11.6 rebounds, 4.4 assists and 2.3 blocks per game. Considered a five-star recruit by Rivals.com, Powell was listed as the No. 8 power forward and the No. 25 player in the nation in 2010.
College career
As a freshman at Stanford in 2010–11, Powell earned Pac-10 All-Freshman Team honors. In 31 games, he averaged 8.1 points and 5.2 rebounds per game. As a sophomore in 2011–12, the Cardinal won the NIT championship, and Powell earned Pac-12 All-Academic Honorable Mention selection. In 35 games, he averaged 5.8 points and 4.6 rebounds per game. As a junior in 2012–13, Powell earned second-team NABC All-District, first-team All-Pac-12, and Pac-12 All-Academic second-team honors. He was also named the Pac-12 Most Improved Player of the Year. In 34 games, he averaged 14.9 points to go with 8.4 rebounds per game. As a senior in 2013–14, Powell earned first-team All-Pac-12 honors for the second straight year and was named to the NCAA All-South Regional Team. He was also named the Pac-12 Scholar-Athlete of the Year and a Pac-12 All-Academic Honorable Mention selection. In 36 games, he averaged 14.0 points and 6.9 rebounds per game.
On December 18, 2014, Powell was traded, along with Rajon Rondo, to the Dallas Mavericks in exchange for Jae Crowder, Jameer Nelson, Brandan Wright, a 2015 first-round pick and a 2016 second-round pick. On January 14, 2015, he scored a season-high 11 points on 5-for-7 shooting in a loss to the Denver Nuggets. He was assigned multiple times to the Texas Legends during his rookie season. In July 2015, Powell joined the Mavericks for the 2015 NBA Summer League. On November 3, 2015, he recorded his first career double-double with 10 points and 10 rebounds in a loss to the Toronto Raptors. Four days later, he recorded a then career-high 15 points and 7 rebounds in a 107–98 win over the New Orleans Pelicans. He tied his career high of 15 points on January 17, 2016 in a loss to the San Antonio Spurs. On March 28, 2016, Powell made his first NBA start and scored a career-high 16 points in a 97–88 win over the Denver Nuggets. On July 8, 2016, Powell re-signed with the Mavericks. On December 3, 2016, he set a new career high with 17 points in a 107–82 win over the Chicago Bulls. On April 9, 2017, he scored 21 points against the Phoenix Suns. On January 3, 2018, Powell tied his career high with 21 points in a 125–122 loss to the Golden State Warriors. On February 28, 2018, he again tied his career high with 21 points in a 111–110 overtime loss to the Oklahoma City Thunder. On March 6, 2019, Powell set a career high with 26 points in a 132–123 loss to the Washington Wizards. On April 3, 2019, he scored 25 points in a 110–108 loss to the Minnesota Timberwolves. After exercising his option for the 2019–20 season, he signed a contract extension with the Mavericks on July 6, 2019. On December 4, 2019, Powell set a season-high 24 points while recording five rebounds, four assists, one steal and two blocks in a 121–114 win against the Minnesota Timberwolves. He had a perfect shooting night, going 9 of 9 from the field and 2 of 2 from the three-point line. Once the fourth quarter started, Powell experienced a left arm injury and got ruled out of the game. On January 21, 2020, in a game against the Los Angeles Clippers, Powell suffered an Achilles tendon injury while attempting to drive to the basket.
