Porter was selected with the 30th overall pick in the 2019 NBA Draft after one collegiate season at USC. He made his NBA debut during the opening game of the season, Oct. 23 against the Magic. Porter played 17 minutes and recorded two assists, one rebound and one steal. Porter had his first double-digit scoring game Nov. 8 against the Wizards when he scored 13 points (5-11 FG, 0-3 3Pt, 3-3 FT). He had his first 20-point scoring effort Dec. 11 against the Rockets when he scored 24 points (9-15 FG, 6-9 3Pt). Porter scored his career-high 30 points (9-18 FG, 4-7 3Pt, 8-10 FT) Feb. 24 in a game against the Heat. He also posted eight rebounds, three assists and three steals in 41 minutes. His other career highs stood at nine rebounds, seven assists, three steals and two blocks. Porter's longest streak of double-digit scoring was seven games from Jan. 28 through Feb. 12. He averaged 16.1 points on 11.6 shots, 2.9 rebounds and 2.4 assists in 27.6 minutes. Overall during his rookie campaign, Porter averaged 10.0 points, 3.2 rebounds and 2.2 assists in 23.2 minutes. He shot 44.2 percent from the field, 33.5 percent from three and 72.3 percent from the free-throw line.