Born in Brooklyn and raised in Manhattan where he attended The Trinity School, the handsome, blond Diamond was bitten by the acting bug at an early age. He began taking lessons before he was in high school and won bit parts in a 1974 "ABC Afterschool Special" entitled "Sara's Summer of the Swans" and the film "Two Minute Warning" (1976). He attended the University of North Carolina at Chapel Hill for two years before transferring to the prestigious Juilliard School. While still studying, he was cast by producer David Puttnam as Virgil, a crew member aboard "Memphis Belle" (1990), a fictional version of the B-17's bombing raid over Germany during WWII.