After four seasons at Utah State, Merrill was selected with the 60th overall pick in the 2020 NBA Draft. He made his NBA debut for the Bucks on Dec. 23 against the Celtics, playing five minutes. He recorded his first stats on Christmas against the Warriors. Merrill played eight minutes and posted six points, four assists and one steal. Overall, he appeared in 30 games (two starts) and averaged 3.0 points and 1.0 rebounds in 7.8 minutes. He shot 44.7 percent from three. On March 26 against the Celtics, Merrill scored a career-high 15 points. One day later, Merrill handed out a career-high five assists. On April 9 against the Hornets, he grabbed a career-high six rebounds. Against the Bulls on May 16, he recorded a career-high three steals. Merrill also appeared in eight playoff games for Milwaukee, who went on to win the NBA title. In his 30 total minutes, the rookie posted five points, five rebounds, four steals and one assist.