In addition to the comic strips and graphic novels based on "Modesty Blaise", O'Donnell published two collections of short stories and twenty novels. He wrote a play that was widely performed in the 1980s, "Mr. Fothergill's Murder", and wrote for television and film. He wrote for women's magazines and children's papers early in his career. His most famous creation, "Modesty Blaise", was first published in 1963 in comic strip form. For the first seven years, the strip was illustrated by Holdaway until his death in 1970. Enrique Badia Romero then became the artist, and except for a seven-year period (1979–86) he drew the strip until it ended in 2001.