Marshall died Tuesday of complications from a lung infection. The director had suffered a stroke earlier and was in a California hospital, Michelle Bega told dpa.
Born in 1934, he was the creator and executive producer of the wholesome TV sitcom Happy Days, set in an idealised 1950s Wisconsin, which ran for a decade from 1974 and has remained popular in reruns.
His 1990 directorial hit Pretty Woman starred Richard Gere opposite then newcomer Julia Roberts playing a streetwalker who undergoes a transformation to mingle in Los Angeles high society.
He went on to direct a dozen more movies, most in the romantic comedy genre, including Runaway Bride (1999) and The Princess Diaries(2001).
His latest film, Mother's Day, stars Roberts, Jennifer Aniston, Kate Hudson and other stars in an ensemble cast. It was released in the US in April, and will reach German cinemas in August.
- DPA