He appeared on a range of television shows, including Trapper John, M.D., T. J. Hooker, Kate & Allie, The Equalizer, Tales from the DarkSide, and The Cosby Mysteries. In 1992, he was cast in the lead role of Commander Jeffrey Sinclair in the science fiction television series Babylon 5. He appeared throughout the show's first season in 1994, and made guest appearances in the second and third seasons. He had two guest roles on Law & Order, but retired from acting and rarely made public appearances.
On September 28, 2012, Straczynski posted that O'Hare had suffered a heart attack in New York City five days earlier, and had remained in a coma until his death that day. Eight months later, Straczynski revealed the circumstances of O'Hare's departure from Babylon 5 at a presentation about the series at the Phoenix Comicon.
