Terms were not disclosed Thursday.
The Grizzlies swapped a future second-round draft pick to Orlando for the 6-foot-10, 220-pound Rabb. Last season at California, Rabb averaged 10.5 rebounds to lead the Pac-12, and he also scored 14 points per game.
Rabb, 20, started 64 of his 65 games in his two seasons at Cal. He was a 2015 McDonald's All-American.
The Grizzlies open camp Tuesday in Memphis.