Mitrou-Long made his NBA debut four days later, recording a three-pointer in a blowout 107–83 loss to the Denver Nuggets. However, on January 13, 2018, Mitrou-Long was waived from the Jazz in order to sign former college teammate Georges Niang. He was re-signed by the Jazz on February 11, 2018 to a 10-day contract. After his first 10-day contract expired on February 21, he signed a second 10-day contract with the Jazz three days later. On January 16, 2018, Mitrou-Long was reacquired by the Salt Lake City Stars. He returned to Salt Lake City once again on February 21, 2018, after his 10-day contract expired. Mitrou-Long left Salt Lake City once again for his second 10-day contract with the Utah Jazz, and returned to Salt Lake City after the second 10-day contract expired. He averaged 18.0 points, 6.1 rebounds, and 4.6 assists per game with Salt Lake City. In July 2019, Mitrou-Long joined the Cleveland Cavaliers for the 2019 NBA Summer League. On July 31, 2019, Mitrou-Long signed a two-way contract with the Indiana Pacers. On November 18, 2019, Mitrou-Long scored a career-high 12 points while getting three rebounds, three assists and one steal in a 115–86 win against the Brooklyn Nets. Mitrou-Long was born on August 3, 1993, in Mississauga, Ontario, to Jersey Long and Georgia Mitrou. His father is of Trinidadian descent while his mother is a Greek Canadian. Mitrou-Long has three siblings and six half-siblings. His brother, Elijah Mitrou-Long, previously played college basketball for Mount St. Mary's University before transferring to the University of Texas in his junior year. After one year with the Longhorns, he transferred to the University of Nevada, Las Vegas. In summer 2015, Mitrou-Long decided to display his full last name on his jersey to honor his mother; up to that point his jersey had only his father's name on it.