Reed Diamond attended the University of North Carolina before transferring to the prestigious Juilliard School. While still studying, he was cast by producer David Puttnam as Virgil, a crew member aboard Memphis Belle, a fictional version of the B-17's bombing raid over Germany during WWII.

Even before graduating from Juilliard, Diamond had been cast in a supporting role to Jessica Lange in the CBS/Hallmark Hall of Fame presentation of Willa Cather's O Pioneers! More TV work followed, including a recurring role on Class of '96 (Fox) and key roles in Ironclads (TNT) and another Hallmark presentation, Blind Spot (CBS). He also guest starred in an episode of Law & Order (NBC).

In 1995, Diamond joined the cast of NBC's Homicide: Life on the Street and, that same year, he was seen in the Sylvester Stallone feature Assassins, as well as in three TV movies: Awake to Danger, Her Hidden Truth (both NBC) and Secrets (ABC). Diamond has guest starred in numerous television shows including CBS's Judging Amy, FX Networks The Shield and NBC's The West Wing. In 2003 he played Officer David Burress in the feature film re-make of the popular TV series S.W.A.T, starring Colin Farell. In 2004, he appeared in the blockbuster hit Spider-Man 2, starring Tobey Maguire.