Coming out of high school, Reddish was rated as a five-star recruit and considered one of the top players in his class, earning Mr. Pennsylvania Basketball in his senior year, in addition to being named to the 2018 McDonald's All-American Boys Game, 2018 Jordan Brand Classic and 2018 Nike Hoop Summit.

[1] As a junior, Reddish averaged 16.2 points per game and led the Moose to a Friend's School League title.

[7][8] On September 1, 2017, Reddish committed to Duke University, joined by fellow top-3 recruits RJ Barrett and Zion Williamson.

[17] Reddish appeared in 36 total games for Duke and averaged 13.5 points, 3.7 rebounds and 1.9 assists while shooting 33% from three-point range.

[22] On October 24, 2019, Reddish made his NBA debut, started in a 117–100 win over the Detroit Pistons with one point, seven rebounds, an assist and a steal.

[28] Coming into the 2022–23 season, Knicks head coach Tom Thibodeau was unsure of the role Reddish would play in his rotation.

[29] After earning a few starts in the beginning of November, Thibodeau announced on December 6, 2022, that Reddish had fallen out of his nine-man rotation.

[31] He made his Trail Blazers debut the next day, recording 11 points, two rebounds and two assists in a 138–129 loss to the Oklahoma City Thunder.

[38] Reddish has a younger brother, Aaron, who played high school basketball for fellow NBA player Collin Sexton's former team, the Pebblebrook Falcons in Mableton, Georgia and currently a junior for the Albany Great Danes.