Milton was selected by the Dallas Mavericks in the second round (54th pick overall) in the 2018 NBA draft. He was subsequently traded to the Philadelphia 76ers for the rights to the 56th and 60th picks, Ray Spalding and Kostas Antetokounmpo, respectively. On July 26, Milton signed a two-way contract with Philadelphia, which would split his playing time between the 76ers and their NBA G League affiliate, the Delaware Blue Coats. Milton made his NBA debut on November 30, 2018 against the Washington Wizards, scoring five points and recording two assists. As a rookie, Milton appeared in 20 games for the Sixers, averaging 4.4 points, 1.8 rebounds, and 0.9 assists in 13.4 minutes per game. Milton scored a career high 13 points when playing against the Orlando Magic on March 25, 2019. Milton also averaged 24.9 points (4th-best in the G-League), 5.2 assists, and 4.8 rebounds per game in 27 contests for the Blue Coats.