Born as Lois Mae Green in Deer Lodge, Montana, she appeared in 70 movies from 1932 through 1966. She was discovered by Ida Koverman, secretary to MGM mogul Louis B. Mayer, after she saw a poster featuring Parker portraying Father Time. She attended Pasadena schools and graduated from John Muir High School. Her original aspirations were in the fine arts and illustration.

She had a successful career at MGM, RKO and Columbia including important roles such as the tragic Beth in the original Little Women, among many other film appearances including Frank Capra's Lady for a Day and Gabriel Over the White House; Sequoia; The Ghost Goes West, opposite Robert Donat; and Rasputin and the Empress, with fellow players, the Barrymore siblings (John, Ethel, and Lionel) in the only movie they all made together. In 1939, she starred opposite Stan Laurel and Oliver Hardy in RKO's The Flying Deuces.