[2] He is the son of Maurice Marshall, who was a professional boxer and is now a basketball coach at an elementary school, and Rayna Whitted, who works at Providence Hospital in Washington, D.C. His name means "strong warrior" in Arabic and was a nickname of his father's.

As a sophomore, he transferred to Eleanor Roosevelt High School to play under coach Brendan O'Connell but was academically ineligible his first year.

He led Eleanor Roosevelt to a 23–3 record and scored 27 points to lead the Raiders past Perry Hall High School 69–59, in the Maryland 4A state semifinals.

[6] Marshall received scholarship offers from Pittsburgh, South Carolina, and Virginia Tech, but committed to playing college basketball for Xavier because he liked the culture.

[3] Marshall earned his first Big East player of the week honors on December 31, 2018, after scoring 19 points, grabbing a career-high 14 rebounds, and dished out four assists in a 74–65 win against DePaul.

[13] Coming into his junior season, Marshall was named to the preseason First Team All-Big East and was on the watchlist for the Julius Erving Award.

[16] On February 1, 2020, Marshall contributed 19 points, 10 rebounds and four assists in a 74–62 upset of tenth-ranked Seton Hall despite playing with the flu.

[17] Marshall hit the game-winning three-pointer with 4.5 seconds left in a 66–63 win at Georgetown on March 1, finishing with 20 points and 10 rebounds.

[25] In his rookie season, Marshall averaged 7.7 points and 4.6 rebounds per game for the Pelicans, shooting 39.2 percent from the field.