She broke into films and Broadway at around the same time, with extra roles in the 1928 play Salvation and the 1929 film short Harry Fox and His American Beauties. Throughout the 1930s she alternated her time between Broadway and movie roles. Her large size, matronly carriage and distinctive voice (which would have been excellent for cartoon voiceovers), made her eminently castable, and she worked constantly until she retired. She was often cast as rich dowagers in her early years, but she was especially adept at plain-spoken, fussy, earthier types, so she eventually specialized in playing ill-tempered domestics and landladies, and (because of her country accent) especially frontier women in musicals and westerns, almost invariably comical ones.
She is in Stella Dallas (1937), both the stage and screen versions of Dead End (1935-1937), and both the stage and screen versions of The Women (1936-1939), five films with Wallace Beery starting with Barnacle Bill (1941), Meet Me in St. Louis (1944), The Harvey Girls (1946), Summer Stock (1950), Friendly Persuasion (1956), and of course the film series she became best known for, Ma and Pa Kettle (1947-1957) (read more about that series here). And this is just the tip of the iceberg; she gave memorable turns in dozens more movies than this.
While she was briefly married, Main admitted in an interview to having had lesbian affairs, one of which is widely believed to have been with Spring Byington. Her last performance was in a 1958 episode of Wagon Train. Her last public appearance was the year before she died, at the world premiere of the MGM compilation film That’s Entertainment.
For more on vaudeville history, consult No Applause, Just Throw Money: The Book That Made Vaudeville Famous, available at Amazon, Barnes and Noble, and wherever nutty books are sold.