Early life and education

Diamond was born in Brooklyn, the son of Allison, an astrologer, and Bob Diamond, a stage manager and director of shows such as The Joe Franklin Show. He was raised in Manhattan and attended the Trinity School.

Diamond attended the University of North Carolina at Chapel Hill for two years, then studied acting at the Juilliard School, where he was a member of the Drama Division's Group 20 (1987-1991).

Career

As a child, Diamond had small parts in the ABC Afterschool Special Sara's Summer of the Swans (1974) and the film Two Minute Warning (1976). His early roles as an adult included guest starring on Law & Order and Class of '96, and such films as Memphis Belle (1990), Clear and Present Danger (1994) and Her Hidden Truth (1995).

His first big break came in 1995 when he joined the cast of Homicide: Life on the Street as Det. Mike Kellerman. Diamond was a regular cast member for Seasons 4-6 before Kellerman was written out at the end of Season 6; but he reprised the role for a two-episode story in the final Season 7. In 2000, a feature-length TV movie was produced to wrap up the series, which saw the return of all the major cast, including Diamond. He made a brief reappearance as a police detective in the pilot episode of the 2002 pilot of the controversial series The Shield, as Detective Terry Crowley. He was credited as one of the main cast members and featured prominently in promotional pictures of the show, so as to surprise viewers when he was murdered at the end of the first episode. Recent roles include a re-make of High Noon (2000); Three Days; S.W.A.T. (2003, directed by Diamond's Homicide co-star Clark Johnson); Spider-Man 2 (2004); and Good Night, and Good Luck (2005).

As well as playing the recurring role of Stuart Collins on Judging Amy from 1999 to 2003, Diamond has guest starred on Crossing Jordan, The West Wing, Medium, Numb3rs, CSI: Crime Scene Investigation, Stargate SG-1, Without a Trace, The Mentalist, 24, and Common Law. He portrayed Inspector Jack Vasser in the Fall 2007 NBC series Journeyman until the cancellation of the show in December 2007. As of spring 2010, Diamond has joined the cast of the TNT series Franklin & Bash. In 2010, he voiced Barnes in Firebreather. In 2011, he had a part in Moneyball, as a general manager of the Cleveland Indians. In 2012 he played Robert Yule, Dr. Ryan's fiancee in Common Law on the USA network. He is currently playing senior HYDRA agent Dr. Daniel Whitehall in Marvel's Agents of S.H.I.E.L.D. and played toymaker Harold Ballinger in the mystery series Wayward Pines.

He had a pivotal role as plantation owner Tom Macon on season one of WGN's series Underground.

Personal life

Diamond was married to Fredrika Kesten from 1995 to 1997. Since 2004, he has been married to actress Marnie McPhail.

Filmography

Year	Title	Role	Notes
1990	Memphis Belle	Sgt. Virgil Hoogesteger
1994	Clear and Present Danger	Coast Guard Chief
1995	Assassins	Bob
2001	The Breed	Phil
2003	S.W.A.T	Officer David Burress
2004	Spider-Man 2	Algernon
2005	Madison	Skip Naughton
2005	Good Night, and Good Luck	John Aaron
2005	Berkeley	Ralph
2006	The Darkroom	The Man
2007	Adrenaline	Voice of Harvey
2007	Meet Bill	Paul
2011	Moneyball	Mark Shapiro
2012	Much Ado About Nothing	Don Pedro

Television

Year	Title	Role	Notes
1988	ABC Afterschool Special	Gary Farrell
1991	Ironclads	Leslie Harmon
1991	Loving	Garth Watkins
1991 & 2005	Law & Order	Mr. Klein / Christopher Baylor
1992	O Pioneers!	Emil
1993	Boy Meets Girl
1993	Class of '96	Stephen Sinclair
1993	Blind Spot	Charlie
1994	Under Suspicion	Bill Palmer
1995	Away to Danger	Jeffrey Baker
1995	Secrets	Thomas Rafferty
1995	Her Hidden Truth	Clay Devereaux
1996	Full Circle	Harry Winslow
1997	Mighty Ducks	Falcone
1997	Indefensible: The Truth About Edward Brannigan	Eddie Brannigan Jr.
1995-98	Homicide: Life on the Street	Detective Mike Kellerman
1999-2003	Judging Amy	Stuart Collins	19 episodes
2000	Homicide: The Movie	Private Investigator Mike Kellerman
2000	919 Fifth Avenue	Ben Constant
2000	High Noon	Harvey Pell	TV movie
2001	The Huntress	Mike Kaputo
2001	The Breed	Phil
2001	Family Law	Alan Caldwell
2001	Three Days	Andrew Farmer
2002	Scared Silent	Doug Clifson
2002	Presidio Med	Will Raymond
2003	The Twilight Zone	Boyfriend
2002	The Shield	Terry Crowley
2004	Crossing Jordan	Gordon Kimball
2004-05	The West Wing	Dr. Mike Gordon
2005	Medium	Jared Swanstrom
2005	CSI: Crime Scene Investigation	Ray Lester
2005	Numb3rs	Dr. Kenneth Hill
2006	Faceless	Marcus Ambrose
2006	Stargate SG-1	Major Bryce Ferguson
2006	Without a Trace	Eric Hayes
2006	Vanished	Therapist
2006	Ghost Whisperer	Dr. Martin Schaer
2007	October Road	Gavin Goddard
2007	Journeyman	Jack Vasser
2008	Criminal Minds	Craig Bridges
2009	Drop Dead Diva	Chad Billmeyer
2009	Monk	FBI Agent Stone
2009	Castle	Dr. Cameron Talbot
2009	Cold Case	Darren Musk
2009-10	Dollhouse	Laurence Dominic
2010	24	Jason Pillar
2010	Firebreather	Barnes (voice)
2011	Law & Order: LA	Franklin Citron
2011-13	The Mentalist	CBI Agent Ray Haffner	5 episodes
2011-14	Franklin & Bash	Damien Karp
2012	Desperate Housewives	Greg Limon
2012	The Glades	Councilman Greg Dousett
2012	Common Law	Robert Yule
2012-13	Bones	FBI Special Agent Hayes Flynn	4 episodes
2012	Revolution	Sergeant Wheatley
2013	White Collar	Cole Edwards
2014, 2016	Agents of S.H.I.E.L.D.	Werner Reinhardt / Daniel Whitehall	8 episodes
2015	Wayward Pines	Harold Ballinger
2014-15	State of Affairs	Jules	3 episodes
2016-present	Underground	Tom Macon

[ Source: Wikipedia ]