Louise Campbell McMahon (1911-1997) was born in Chicago and trained for a career on the stage at De Paul University and the Chicago School of Expression. She made her Broadway debut soon afterward, as a maid in Three Men on a Horse. In 1942 she starred in Guest in the House, which ran for two years.
Paramount Studios awarded Louise Campbell a motion picture contract in 1937, and during the next 10 years she appeared with Fred MacMurray and Ray Milland in Men With Wings, with Bing Crosby in The Star Maker, and John Barrymore in Night Club Scandal. In 1938, she married actor Horace McMahon, also a Lamb, who would later star on the television series Naked City and Detective Story. Their daughter, Martha McMahon Pappas, became a Lamb around 1980.
She took a 15-year break from acting to raise two daughters and a son. In 1979 she joined The Lambs. Her last New York stage appearance was in a 1982 production of Uncle Vanya, starring Michael Moriarty, at the Public Theater.
Louise Campbell McMahon’s Broadway biography is here.