Furst rose to prominence in National Lampoon's Animal House (1978), where he played the role of Flounder. He got the role during a side-job delivering pizzas. One of the film's producers saw his headshot taped to the inside of a pizza box and auditioned him. Furst reprised the role of Flounder in the short-lived TV spin-off, Delta House (1979).
Furst then became known for his role as Dr. Axelrod on St. Elsewhere (1983-88). His character was seen as jovial and bumbling, but as the series proceeded became more competent and respected. His character was killed off shortly before the series itself terminated.
During the second season (1994-95), Vir became a significantly more complex and rounded character when Straczynski gave him the role of Londo's conscience, his "good angel" as contrasted to the "evil angel" of Morden (Ed Wasser). The rivalry between the two characters culminated in Vir's eventual victory and, in the final episode of the series, his succession to Londo as Emperor of the Centauri Republic. His character went on to play a major role in the spin-off novels, particularly Peter David's well-received Legions of Fire trilogy where Vir helps liberate Centauri Prime from the Drakh.
Stephen Furst played the role with vigour and conviction. A passionate liberal, he and arch-Republican Jerry Doyle (who played Mr. Garibaldi) would engage in political debates on set which other castmembers enjoyed (to varying degrees). Furst was also encouraged by his newfound fame with the show's viewers and growing health concerns (he had been diagnosed with Type 2 diabetes just a few years earlier) to get into better shape, visibly shedding weight between seasons.
Furst also began a new career as a director thanks to Babylon 5. He directed three of the show's best-received episodes (The Illusion of Truth, The Deconstruction of Falling Stars and The Corps is Mother, the Corps is Father) as well as two episodes of its spin-off series, Crusade.
He continued to work as a director on TV movies for SyFy, as well as occasionally appearing in guest roles on other shows.
Furst's death brings the number of premature deaths of the Babylon 5 main cast to a startling six. Richard Biggs (Dr. Stephen Franklin) passed away in 2004, followed by Andreas Katsulas (Ambassador G'Kar) in 2006, Jeff Conaway (Security Chief Zack Allen) in 2011, Michael O'Hare (Commander Sinclair) in 2012 and Jerry Doyle (Mr. Garibaldi) almost exactly a year ago. Other people involved in the show have also passed away, such as recurring actor Tim Choate (Zathras) in 2004 and CGI pioneer Ron Thornton last year, who created a lot of the show's distinctive visual look.