Mortimer wrote over a dozen novels during her career, focusing on upper middle-class life in British society. She had one novel, "Johanna", published under the name Penelope Dimont. Then as Penelope Mortimer she wrote "A Villa in Summer" (1954, Michael Joseph), which received critical acclaim. Subsequent novels included "Daddy's Gone A-Hunting" (1958, republished in 2008 by Persephone Books) and "The Pumpkin Eater" (1962), which dealt with a troubled marriage and had success as a film released in 1964 starring Anne Bancroft.