 Diamantopoulos began appearing in TV commercials and professional theatre productions at the age of 9 and by the time he turned 18, he had left home to partake in a series of U.S. national tours.A short time later, he worked on Broadway where he played leading parts in "The Full Monty" (2002) and "Les Misérables" (2003).Diamantopoulos attended East York Collegiate Institute.