Diamond was born and raised in New York City. He attended school at UNC-Chapel Hill and then went on to study acting at The Juilliard School in New York. His professional career began in 1990 with his co-starring role in the movie Memphis Belle (1990). Following that, he appeared on Broadway, and in many television movies, and guest-star roles on TV.
He is probably best known for playing "Detective Mike Kellerman" on the critically acclaimed NBC television show Homicide (1993).
Diamond most recently guest-starred on television in, "October Road," Ghost Whisperer (2005), Vanished (2006), FBI - Portés disparus (2002), Numb3rs (2005), New York - Police judiciaire (1990), "CSI", Médium (2005), À la maison blanche (1999), Amy (1999), Preuve à l'appui (2001), and The Shield (2002).
Some of his most notable movie credits include Good Night, and Good Luck (2005), Spider-Man 2 (2004) and S.W.A.T. unité d'élite (2003).
Diamond resides in Los Angeles with his wife, actress Marnie McPhail.
