Although born in Virginia, Martin settled with his family in Buffalo, New York when he was in the fourth grade. At his new school, he was cast in his first play and was hooked. After attending the Buffalo School for Visual and Performing Arts and NYU's Tisch School of the Arts, he embarked on an acting career that included stints on daytime TV (CBS' "Guiding Light") and regional theater. Like many struggling thespians, Martin waited tables to make ends meet. Hired to work at the Moondance Diner in NYC, he was trained by Jonathan Larson, who a few short years later saw a musical of his produced--"Rent". Martin had already twice appeared on Broadway in small roles with the National Actors Theater and almost did not audition for his star-making role because he did not want to appear in a musical. He finally agreed to try out for the show to repay the show's casting director who had previously hired him on several occasions. Martin turned in a beautifully rendered portrayal of an emotionally bruised man who unexpectedly finds love with a drag queen in the musical.

Following this high profile stage turn, Martin found his career shifting gears. He began landing roles in primetime programs, including a regular stint as a newly married staff psychologist on the short-lived Fox drama "413 Hope Street" (1997-98). He segued to the big screen as one of the kitchen workers in the titular "Restaurant" (1998) before landing a guest spot as a doctor being sued for questionable practices in a 1998 episode of "Ally McBeal". His character and the lady lawyer clicked and entered into a brief romance that was abruptly ended. In 1999, Martin lent his easy charm to a reprise of the role in a story arc that found the duo attempting to rekindle their relationship. There was undeniable chemistry in the pairing and only minor stirrings over this interracial romance. (In fact, the only negative comments about the love story was that no one addressed the issue.) While some fans might have wished that Dr. Butters and Ally continued their romance, fate had other plans.

Martin was tapped by producer Dick Wolf to replace the departing Benjamin Bratt as a police detective in "Law & Order" beginning in the fall of 1999. As Det. Green, he became a mainstay of the series, partnered first with Jerry Orbach's Lennie Briscow and then with Dennis Farina's Joe Fontana. With his hiatuses, he appeared in a handful of side projects, including "Season of Youth" (2002) and the NBC musical telepic "A Christmas Carol" (2004), playing the Ghost of Christmas Present to Kelsey Grammer's Scrooge. In 2005 Martin's character was temporarily written off "Law & Order"--Green was the shot and nearly killed--to accomodate his shooting schedule for director Chris Columbus' big-screen version of "Rent' (2005), for which he was particularly effective reprising his role as Tom Collins, despite the movie's overall uneven quality.