Since 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 ABC 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 TV special Ringo.Hooperman was Ritter's first regular television role after Three's Company.
Ritter attended Hollywood High School, where he was student body president.
Ritter was a member of Phi Gamma Delta fraternity at USC. After his graduation from USC in 1970, his first TV acting experience was a campus revolutionary in the TV series Dan August starring Burt Reynolds and future Three's Company co-star Norman Fell.
While still in college, Ritter traveled to the United Kingdom, the Netherlands, and West Germany to perform in plays. Ritter made his film debut in the 1971 Disney film The Barefoot Executive.
Ritter co-starred opposite Joyce De Witt and Suzanne Somers; however, Somers left due to a contractual dispute in 1981.
Jenilee Harrison and then Priscilla Barnes filled Somers's role.