Reddick was born in Baltimore, Maryland, where he attended Friends School of Baltimore in the class of 1980. He studied music and musical theory as a teenager and enrolled at the Yale School of Drama in 1991.
Reddick is most recognizable as Cedric Daniels in The Wire, Special Agent Phillip Broyles in sci-fi drama Fringe, Detective Johnny Basil in Oz and as Matthew Abbadon in Lost. Of these roles, Fringe and Lost have become cult hits, with Fringe being his longest television role to date with 90 episodes of the show including Reddick.
Reddick started his television career in 1996 as Oscar Griffin in an episode of New York Undercover. Since then, he has appeared in television hits such as the Law & Order franchise, CSI: Miami, Numb3rs, Intelligence and American Horror Story: Coven. He appeared in two episodes of The Blacklist.
In 2007, Reddick released Contemplations & Remembrances, a smooth and relaxing collection of music.