Houston Rockets (2015–2017) On June 25, 2015, Harrell was selected by the
Houston Rockets in the second round of the
2015 NBA draft with the 32nd overall pick. On September 19, 2015, he signed a three-year deal with the Rockets. He made his debut for the Rockets in the team's season opener against the
Denver Nuggets on October 28, recording eight points and three rebounds in a 105–85 loss. Two days later, he scored 17 points in a loss to the
Golden State Warriors. On November 13, he made his first career start, scoring five points in just under 13 minutes of action, as the Rockets were defeated by the Denver Nuggets 107–98. On March 28, 2016, Harrell received a five-game
NBA D-League suspension without pay for pushing a game official. During his rookie season, he received multiple assignments to the
Rio Grande Valley Vipers, the Rockets' G-League affiliate. On November 2, 2016, Harrell had a 17-point, 10-rebound effort off the bench in a 118–99 win over the
New York Knicks. On December 21, 2016, against the
Phoenix Suns, Harrell made his first start of the season and second of his career. He scored 17 points as a result, tying a career high. On December 30, he set a new career high with 29 points in a 140–116 win over the
Los Angeles Clippers. On January 8, 2017, he had 28 points in 26 minutes off the bench on 12-of-13 shooting in a 129–122 win over the
Toronto Raptors.
Los Angeles Clippers (2017–2020) On June 28, 2017, the
Los Angeles Clippers acquired Harrell,
Patrick Beverley,
Sam Dekker,
Darrun Hilliard,
DeAndre Liggins,
Lou Williams,
Kyle Wiltjer, and a 2018 first-round pick from the Houston Rockets in exchange for
Chris Paul. On January 11, 2018, he scored a season-high 25 points in a 121–115 win over the
Sacramento Kings. On July 24, 2018, Harrell re-signed with the Clippers on a two-year, $12 million contract. On October 26, 2018, Harrell scored a career-high 30 points off the bench in a 133–113 win over the
Houston Rockets. On February 22, 2019, he matched his career high with 30 points in a 112–106 win over the
Memphis Grizzlies. Three days later, he set a new career high with 32 points in a 121–112 win over the
Dallas Mavericks. On November 6, 2019, Harrell set a new career high of 34 points, alongside 13 rebounds and five assists, in a 129–124 loss to the
Milwaukee Bucks. On November 24, he again scored 34 points, alongside twelve rebounds, two assists and two blocks, in a 134–109 win over the
New Orleans Pelicans. On January 5, 2020, Harrell scored 34 points, alongside six rebounds and three assists, in a 135–132 win over the
New York Knicks. During the 2019–20 season, Harrell averaged career highs in points (18.6) and rebounds (7.1) per game. He was named the
NBA Sixth Man of the Year, and was awarded the
NBA Hustle Award. The Clippers fell in seven games during the second round of the playoffs after the
Denver Nuggets came back from a 3–1 deficit, despite a team-leading 20-point effort from Harrell in Game 7. Harrell averaged 10.5 points and 2.9 rebounds in the playoffs.
Los Angeles Lakers (2020–2021) On November 22, 2020, Harrell signed a two-year, $19 million contract with the
Los Angeles Lakers. On December 22, he made his Lakers debut, putting up 17 points, 10 rebounds, and three assists, in a 116–109 loss to the Los Angeles Clippers. On March 15, 2021, Harrell scored a season-high 27 points, alongside five rebounds and three steals, in a 128–97 win over the
Golden State Warriors. In the first round of the playoffs, the Lakers fell in six games to the
Phoenix Suns, with Harrell only averaging 9.8 minutes a game.
Washington Wizards (2021–2022) On August 6, 2021, Harrell was traded to the
Washington Wizards as part of a package for
Russell Westbrook. Harrell made his Wizards debut on October 20, recording 22 points and nine rebounds in a 98–83 win over the
Toronto Raptors. On December 1, he scored a season-high 27 points, alongside five rebounds and three assists, in a 115–107 win over the
Minnesota Timberwolves.
Charlotte Hornets (2022) On February 10, 2022, Harrell was traded to his hometown team the
Charlotte Hornets in exchange for
Ish Smith,
Vernon Carey Jr., and a 2023 second-round pick. On February 11, Harrell made his Hornets debut, putting up 15 points and six rebounds in a 141–119 win over the
Detroit Pistons.
Philadelphia 76ers (2022–2023) On September 13, 2022, Harrell signed a 2-year deal with the
Philadelphia 76ers. He made his 76ers debut on October 18, scoring two points in a 126–117 loss to the
Boston Celtics. On June 21, 2023, Harrell declined his $1.97 million player option to become a free agent and on July 18, he signed with the 76ers on a 1-year deal. However, on August 2, he suffered an
anterior cruciate ligament (ACL) injury while preparing for the training camp and was waived on October 23. He subsequently missed the entire
2023–24 NBA season and participated in NBA minicamps ahead of the 2024–25 season.
Adelaide 36ers (2024–2025) On September 12, 2024, Harrell signed with the
Adelaide 36ers of the
National Basketball League (NBL) in Australia as an injury replacement player for
Jarell Martin. In his debut for the 36ers on September 22, he recorded 13 points and 13 rebounds in a 102–94 loss to the
Sydney Kings. On October 18, he signed with the 36ers for the rest of the
2024–25 season. On October 25, he had 36 points, 16 rebounds and five blocks in a 99–93 overtime win over the
Cairns Taipans. On November 25, he was suspended for three games and received fines totalling $3,685 following striking and melee incidents that occurred during Adelaide's game against
Melbourne United on November 17. He went on to earn
All-NBL Second Team honors. In 28 games, he averaged 20.5 points, 9.3 rebounds, 2.0 assists and 1.1 blocks per game.
Xinjiang Flying Tigers (2025) In early February 2025, Harrell reportedly signed with the
Zhejiang Golden Bulls of the
Chinese Basketball Association. After not joining the team before the scheduled date of February 22, he signed with the
Xinjiang Flying Tigers on March 13, replacing
Rob Edwards. In 13 games for Xinjiang to finish the
2024–25 season, he averaged 11.9 points, 4.4 rebounds and 1.8 assists per game. On June 25, the
China Anti-Doping Agency announced that a test Harrell performed on April 15 showed positive for
carboxy THC. On May 28, 2025, Harrell re-signed with the
Adelaide 36ers for the
2025–26 NBL season. However, he was released from his contract by the 36ers on September 25, 2025, after Harrell was found to have used
tetrahydrocannabinolic acid while playing in China in April 2025.
Gigantes de Carolina (2025) On May 15, 2025, Harrell signed with
Gigantes de Carolina of the
Baloncesto Superior Nacional (BSN) for the rest of the
2025 season.
Atléticos de San Germán (2026–present) On January 2, 2026, Harrell signed with
Atléticos de San Germán for the 2026 BSN season. ==National team career==