After graduating from Cambridge and attending drama school, Fellowes honed his craft appearing on stage with various repertory companies as well as making the occasional guest appearance on TV (i.e., "The Duchess of Duke Street"). In 1981, he headed to L.A. and acted in several made-for-television movies, portraying a Nazi in support of Anthony Hopkins' Hitler in "The Bunker" (CBS, 1981), the Emperor Nero in the CBS biblical miniseries "Peter and Paul" (1981) and the Prince Regent in "The Scarlet Pimpernel" (CBS, 1982). Becoming disenchanted by Southern California, Fellowes returned to England, married and established Lionhead Productions, through which he served as associate producer on the syndicated TV drama "A Married Man" (1989), starring Anthony Hopkins.
Although interested in behind the scenes work, Fellowes continued to perform, becoming an in demand character player in projects ranging from "Goldeneye", a 1990 small screen biopic of James Bond creator Ian Fleming (in which he portrayed Noel Coward), to the features "Damage" (1992) and "Shadowlands" (1993). In 1994, he made his screenwriting debut adapting Frances Hodgson Burnett's novel "Little Lord Fauntleroy" into an award-winning miniseries. (It aired in the USA on the Disney Channel in 1995). In a rather odd twist, Fellowes was cast as the Minister of Defence in the James Bond film "Tomorrow Never Dies" (1997). Drawing on his family background, he essayed a titled nobleman in the British miniseries "Aristocrats" (1999) and joined the cast of the BBC series "Monarch of the Glen" in 2000 as a Scottish lord. It was while appearing in the latter that he wrote the screenplay for "Gosford Park". While his success as a writer has brought numerous offers, Fellowes has stated he hopes not to abandon his performing career.