William received the 1998 Tony Award for Best Orchestrations for Ragtime.
Other Broadway and West End credits include: Half a Sixpence (Noël Coward); the revival of Miss Saigon (Prince Edward); Curtains; Mary Poppins; The Secret Garden; Show Boat; Crazy for You; Carousel; Sweet Smell of Success; Oklahoma!; Oliver!; The Witches of Eastwick; My Fair Lady; South Pacific; Betty Blue Eyes and Barnum (Chichester).
He has provided arrangements for Marilyn Horne, James Galway, Placido Domingo and West Side Story Suite for Violin and Orchestra.