Ritter headlined several stage performances. After his graduation from USC in 1970, his first television acting experience was a campus revolutionary in the television series "Dan August" starring Burt Reynolds and future "Three's Company" co-star Norman Fell. Ritter made his film debut in the 1971 Disney film "The Barefoot Executive". He made guest appearances on the television series "Hawaii Five-O", "M*A*S*H", and many others. He had a recurring role as the Reverend Matthew Fordwick on the drama series "The Waltons" from October 1972 to December 1976. Because he was not a weekly cast member, he had time to pursue other roles, which he did until December 1976, when he left for a starring role in the hit sitcom "Three's Company" (the Americanized version of the 1970s British Thames Television series "Man About the House") in 1977. In 1978, Ritter played Ringo Starr's manager on the television special "Ringo". In 1982, Ritter provided the voice of Peter Dickinson in the animated film "The Flight of Dragons".