Emerson made her Broadway début in Lysistrata
in 1930 when New York theatrical producer Norman Bel Geddes cast Emerson for the role of the amazonian Lamputo.
Emerson made her film début in Smiling Faces (1932) but then returned to the theater. In the 1940s, Emerson became well known as the voice of Elsie the Cow in Borden Milkcommercials on radio.
Standing 6 ft.-2 in. (1.88m), Emerson's most memorable roles were as a circus strongwoman in the film Adam's Rib (1949), lifting actor Spencer Tracy up in the air; a larcenous conspirator in the noirish Cry of the City (1948); and a mail-order bride in Westward the Women (1952). Her most famous role, as sadistic prison matron Evelyn Harper, in Caged(1950) garnered her an Academy Award nomination for Best Supporting Actress.
On television, Emerson guest starred on the series finale ("The Housekeeper") of the sitcom, It's a Great Life, playing a bossy housekeeper who temporarily takes charge while Amy Morgan, played by Frances Bavier, goes on vacation. She also had a regular role in Peter Gunn (1958), for which she received an Emmy nomination, and sitcom The Dennis O'Keefe Show (1959).
Emerson died of liver disease in 1960 at age 62 in Hollywood, California. She is interred in Grace Hill Cemetery in her hometown of Hawarden, Iowa. She never married or had children.