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 and Les Misérables. Diamantopoulos attended East York Collegiate Institute. He portrayed Robin Williams in Behind the Camera: The Unauthorized Story of Mork & Mindy alongside co-star Erinn Hayes. He has guest-starred in several series, including Kevin Hill, Charmed, The Sopranos, Nip/Tuck and Boston Legal. In 2007, he appeared opposite Debra Messing in The Starter Wife, where he played the role of Rodney, the interior decorator. Diamantopoulos had a recurring role on State of Mind. He also guest-voiced on American Dad! in 2009. On the eighth season of 24, he played US President Allison Taylor's Chief of Staff Rob Weiss. He played Frank Sinatra in The Kennedys. Diamantopoulos played Moe Howard in the 2012 The Three Stooges film. He had recurring roles on the NBC sitcoms Up All Night, as Maya Rudolph's on and off lover, Julian; The Office, as Brian, a former member of the show's documentary film crew, and on Arrested Development, as Marky, Lindsay's face-blind environmentalist boyfriend. He has featured in the UK/US television sitcomEpisodes playing the part of TV network boss Castor Sotto, Mr. Chris in the TV adaptation of About a Boy. In 2017 Diamantopoulos starred in the musical Waitress on Broadway. On October 11, 2018, it was revealed by TVLine that Diamantopoulos would have a role in the spinoff pilot for the situation comedyThe Middle playing Sue Heck's mercurial, charming and rich boss Nick.
Personal life
Diamantopoulos grew up splitting his time between Canada and Greece. He is of Greek descent and is a practicing member of the Greek Orthodox church, as well as speaking fluent Greek. He met his wife, actress Becki Newton, in a subway station in New York. The couple married on May 12, 2005. Newton gave birth to their first child, a boy, in November 2010. In 2014 they had a girl.
