Originally from New Jersey, Bart graduated from Rutgers University in 1985 with a Bachelor of Fine Arts degree. From there he has focused mainly on the stage. On Broadway he received Tony and Drama Desk awards for best actor for his portrayal of Snoopy in the 1999 production of “You’re a Good Man, Charlie Brown.” He also had roles in productions such as “Triumph of Love,” “King David,” and “Frogs,” opposite Nathan Lane. Bart appeared on a handful of television series, including “Law & Order,” and it spin-off, “Law & Order: Special Victims Unit,” (NBC). He also appeared on the short-lived series “Bram & Alice” (CBS). He provided the singing voice of Scamp in Disney’s straight-to-video “Lady & the Tramp II: Scamp’s Adventure,” as well as the singing voice for the title character in Disney's theatrically released “Hercules” (1997). He also appeared in “The Insider,” in 1999.

In Mel Brooks’ immensely popular Broadway musical version of his hit film “The Producers,” Bart originated the role of the flamboyant Carmen Ghia in 2001, for which he received Tony and Drama Desk nominations (Bart would also later take on the role of Leo Bloom in the 2003 Broadway production). He reprised the role for the 2005 feature film, along with Nathan Lane and Matthew Broderick. Bart drew raves for his portrayal of a gay housewife in theotherwise panned feature film, “Stepford Wives” in 2004, with a character based on his performance in “The Producers.” That same year, he originated the role of the obsessively creepy pharmacist who becomes fixated with Bree Van de Camp on "Desperate Housewives," a role that tranformed him from an actor with a cachet among stage aficiandos to, if not a household name, a performer recognized by millions of television viewers, leaving the series with panache just after "The Producers" hit theaters. Hot off his film and TV successes, Bart was cast in comedian Jeff Garlin’s independent comedy film “I Want Someone to Eat Cheese With” as well as in “Doubting Thomas,” both set for release in 2006.