Her birth name was either Francesca Marlene de Czanyi von Gerber, while other sources cite Francesca Marlene de Charney von Gerber as her birth name.

She trained as a ballerina as a child and began her career as a chorus dancer. She sang, acted and danced in a number of film musicals, often paired with some of the biggest male musical stars.

Notable early roles included There's No Business Like Show Business (1954) which featured Irving Berlin's music and also starred Ethel Merman, Dan Dailey, Marilyn Monroe, Donald O'Connor, and Johnnie Ray.

Les Girls (1957, directed by George Cukor) with Gene Kelly and Kay Kendall, and Anything Goes (1956), co-starring Bing Crosby, Donald O'Connor, and Zizi Jeanmaire; with screen-play written by Guy Bolton and P.G. Wodehouse.

Gaynor's biggest international fame came from her starring role in the film version of Richard Rodgers and Oscar Hammerstein II's South Pacific, one of the most successful musicals of all time.

For her performance, she was nominated for a Golden Globe Award for best actess. She made films with many other well-known stars, including Ginger Rogers, Frank Sinatra, David Niven, Dan Dailey, Betty Grable and Oscar Levant.

She made her last film in the early 1960s; one of her last films was the United Kingdom production Surprise Package (1960), a musical comedy thriller directed by Stanley Donen. Her co-stars were Yul Brynner and Noel Coward and the film had a theme song by Jimmy Van Heusen and Sammy Cahn.

After her retirement from films, Gaynor remained a popular favorite; she often performed songs at Academy Awards ceremonies, starred in a series of high-rated TV specials, had a This Is Your Life special dedicated to her, and often appeared on television and in local theater.

For several years, Mitzi Gaynor was a top Las Vegas attraction. She also successfully battled cancer. During the 1990's, Gaynor also became a featured columnist for the influential newsmagazine The Hollywood Reporter.