A dark, exotic beauty, Katherine DeMille was a fascinating screen presence in the 1930s and 1940s. She was born in Canada to a Scottish schoolteacher, Edward Gabriel Lester, and his Italian-Swiss wife, Cecile Bianca Bertha (Colani) Lester. Her father was killed in France during World War I, and her mother, who was terminally ill, traveled to California to find Katherine's paternal grandparents and leave her with them. Mrs. Lester died before she could contact her in-laws and Katherine was placed in a Los Angeles orphanage. Constance Adams, the wife of Hollywood's top filmmaker Cecil B. DeMille, was a director of the orphanage. The DeMilles were moved by Katherine's misfortune and decided to adopt her. She became a member of a family that also included the DeMilles' only natural child, Cecilia de Mille; another adopted child, John de Mille; and Richard de Mille, who was actually DeMille's nephew.

Katherine was educated at the Hollywood School for Girls and the Santa Barbara School for Girls. She loved acting in school plays and eventually found work as a movie extra, using the stage name Kay Marsh. DeMille, aware of his daughter's dream of becoming a star, hired her as a script supervisor for his film Four Frightened People (1934) and permitted her to visit the sets of his films and watch his editing process. She secretly auditioned for the role of Pancho Villa's wife, Rosita Morales, in the MGM production Viva Villa! (1934), starring Wallace Beery in the title role. She won the role and impressed the critics with her performance and beauty. Her portrayal of a Mexican maid in The Trumpet Blows (1934) earned her a contract with Paramount Pictures, and she was cast as the villain in Mae West's Belle of the Nineties (1934). Her ability to succeed in films on her own helped her gain her father's admiration as well as a featured role in his next epic, The Crusades (1935). She played Alice, Princess of France, and competed with Loretta Young's Berengaria for the love (and title as consort) of Richard the Lionheart (Henry Wilcoxon). The critics appreciated Katherine's talent and appearance in the lavish DeMille production. Her career was ascending.

After her excellent work in the prestigious DeMille picture, Katherine was finally elevated to leading lady status. Paramount starred her in Drift Fence (1936) and Sky Parade (1936). She was also loaned out to MGM for an uncredited appearance as Romeo's first love, Rosaline, in Romeo and Juliet (1936). 20th Century-Fox cast her in a supporting role in the Barbara Stanwyck-Joel McCrea starrer Banjo on My Knee (1936) and gave her second billing in Charlie Chan at the Olympics (1937). Katherine fell in love with Mexican actor Anthony Quinn and married him in 1937. She was billed third in The Californian (1937) and appeared in Love Under Fire (1937), a Spanish Civil War drama. At Columbia Pictures, she was billed second in the Jack Holt vehicle Under Suspicion (1937). This was followed by a small role in another Spanish Civil War drama, Blockade (1938), and a leading lady role in another Jack Holt vehicle, Trapped in the Sky (1939). Unfortunately, the big studios failed to showcase her talent in notable productions. Her next roles were featured in B movies: In Old Caliente (1939), Isle of Destiny (1940), Ellery Queen, Master Detective (1940), and Dark Streets of Cairo (1940). She returned to Paramount for a role in the Technicolor film Aloma of the South Seas (1941).

The Quinns had five children. She abandoned her film career after the tragic death of their firstborn, Christopher, in 1941. She made a comeback with a leading role in Black Gold (1947), co-starring her husband, and a supporting role as a Native American woman in her father's Unconquered (1947). She also starred in the film noir The Judge (1949). The Quinns divorced in 1965, and Katherine later moved to Tucson, Arizona, where she died of Alzheimer's disease in 1995.