He played college basketball for the Holy Cross Crusaders, Illinois Fighting Illini, and the Duke Blue Devils.
Coach Raym Young invited Grandison to play basketball on its Adidas sponsored AAU team supported by Oakland's very-own Damian Lillard.
This experience permitted, for the first time, Division I coaches to see Grandison compete from May to July 2016, following his graduation from his public high school.
His success at Phillips Exeter led to Grandison being offered a Division-I scholarship to play for Holy Cross, where he ended up committing.
[9] After sitting out the 2019–20 season because of NCAA transfer rules, Grandison started his Illinois career as a bench player.
This proved to be a successful change as Illinois beat the Nittany Lions 79–65, and Grandison started 15 of the final 16 games of the season.
[10][6] With Grandison in the lineup, Illinois moved from 22 to 2 in the AP poll[11] and won the 2021 Big Ten men's basketball tournament.
[16] On 27 October 2023, it was announced that Grandison had signed his first professional contract with Spanish club Menorca on a three-month deal.
His mother, Carina, is from Haaga, Helsinki, Finland, and she had met Grandison's father, James, in California when she was an exchange student in the U.S.[23] He competitively swam growing up for the Oakland Undercurrents and competed in the 50 freestyle at the Junior Olympics.
[24][2] Grandison's maternal grandfather was Nils Mustelin, a Finnish professor of physics and an astronomer, and a former member of the Helsinki city council.