[3] She made her film debut in Cheers for Miss Bishop[2] and appeared in many Warner Bros. films, including Eyes in the Night, Yankee Doodle Dandy playing Nellie Cohan opposite James Cagney, This Is the Army playing the wife of George Murphy and the mother of Ronald Reagan, Rhapsody in Blue, and Nora Prentiss.

In 1951 and 1953, respectively, she starred in the nostalgic musical films On Moonlight Bay and its sequel, By The Light Of The Silvery Moon, as Alice Winfield, Doris Day's mother, opposite Leon Ames.

She appeared in the role of Gertrude Komack on ABC's medical drama Breaking Point in the episode entitled "A Little Anger is a Good Thing".

DeCamp appeared in 2 episodes of The Beverly Hillbillies as Mrs Priscilla Rolfe Alden Smith-Standish, a famous expert on antiquities who befriended the Clampetts.

[5] On July 7, 1946, her Beverly Hills home was damaged when struck by a wing after the experimental XF-11 piloted by Howard Hughes (re-created in the 2004 movie, The Aviator) crashed nearby.

Although a piece of the wing and a part of the neighbor's roof landed in DeCamp's bedroom (where she and her husband were sleeping) they sustained no injuries.

In 2009, an autobiographical book of her life in film and television titled Rosemary De Camp: Tigers in My Lap was published posthumously.