Previously a corporate jet pilot and after a decade as a stockbroker on Wall Street, Doyle made an abrupt career change into acting in 1991, when he moved to Los Angeles. His first television role was on the series "Moonlighting" where he played a potential replacement for Bruce Willis' character. This was followed by a recurring role as a lawyer on the soap opera "The Bold and the Beautiful". "Babylon 5" was his first significant starring role, starring as security officer Michael Garibaldi. Doyle quipped that on "Babylon 5" he was a "Mick from Brooklyn playing a Wop from Mars."