Following one season at Arizona State, Dort signed a two-way contract with the Thunder in early July of 2019 after going unselected in the draft. The 6-foot-3 guard made his NBA debut Dec. 6 in a win over the Timberwolves, posting one rebound and one steal in seven minutes. He scored his first points one game later, Dec. 8 in a 12-point win over Portland, finishing with two points and three rebounds across 20 minutes. On Jan. 18 in a 13-point win over the Trail Blazers, Dort recorded a career-high two assists -- a mark he would reach 10 more times throughout his rookie campaign. Dort scored a career-high 23 points during a 20-point victory over the Kings on Jan. 29, also posting two rebounds, one steal and a career-high one block in 27 minutes. One game later, during a four-point win over the Suns, Dort swiped a career-high three steals, and he reached that mark two more times during the season. On Jun. 24, Dort signed a new multi-year contract with the Thunder. On Aug. 9 in the Orlando bubble, during an 18-point win over Washington, Dort grabbed a career-high 10 boards along with nine points, one assist and one block in 26 minutes. During the NBA bubble, the rookie appeared in seven of eight Thunder seeding games, averaging 9.1 points, 3.9 rebounds and 1.1 steals in 26.1 minutes per game. He appeared in six of OKC's seven playoff games against the Rockets and was tasked with guarding James Harden. Overall, Dort averaged 12.5 points, 3.7 rebounds, 1.0 assists and 1.0 blocks in 29.2 minutes. Notably, in Game 7, Dort recorded 30 points (10-21 FG, 6-12 3Pt, 4-6 FT), four rebounds, one assist and one block in 35 minutes.