The 55-year-old singer was a frequent presence at the Metropolitan Opera between 1987 and 2002, where he starred in such operas as The Rake's Progress, Cosi Fan Tutte, La Traviata, and The Great Gatsby, in which he created the title role. He also created the lead role in Paul McCartney's The Liverpool Oratorio.
Hadley appeared on television in many operas, as well as in the 1988 documentary The Show Boat Story, in which he sang the role of Gaylord Ravenal, in the title role of a 1989 production of Candide, conducted by the show's composer, Leonard Bernstein, and in the 1993 PBS special Sondheim: A Celebration at Carnegie Hall, in which he sang selections from Sweeney Todd. He was also heard on many recordings throughout his career, and won three Grammy Awards.
Hadley is survived by two sons, Nathan and Ryan, and a sister, Joyce Hadley Jenkins. The funeral will be private, but memorial services are being planned.