Walker played basketball for Campbell Hall School in Los Angeles, California, for three years.

[3] He committed to playing college basketball for Colorado over offers from California and Saint Mary's.

[6] On March 20, 2021, Walker scored a freshman season-high 24 points, shooting 5-of-5 from three-point range, in a 96–73 victory over Georgetown at the first round of the NCAA tournament.

[7] As a freshman, he averaged 7.6 points and 4.3 rebounds per game, earning Pac-12 All-Freshman Team honors.

In his Summer League debut, Walker recorded eleven points and seven rebounds in an 81–78 loss to the Detroit Pistons.