Grint will portray Stan Shapiro, a young William Morris mailroom intern who befriended the late Beach Boy. Moretz has accepted the role of Wilson's daughter, Jennifer, who was said to be with her father during many of his darkest times.
The real-life Jennifer Wilson is close to the project, which begins filming in California in mid-June. Wilson and her half-brother Carl will serve as co-producers for the movie.
Vera Farmiga, who received an Oscar nomination for her role in Up in the Air, will also appear in the film as Fleetwood Mac singer Christine McVie, who was Wilson's lover for the last six years of his life before he drowned unexpectedly in 1983.