Peter O'Donnell began writing professionally at the age of 16. Following the Second World War he became involved in comics, with his first work on the James Bond adaptation. During his early years he worked on various comic strips for the daily newspaper before his most popular and well known creation, Modesty Blaise, was first published in 1963. While continuing his work on Modesty Blaise, he also wrote numerous short stories and several novels, including several award-winning romance novels under the pseudonym Madeleine Brent. He also occasionally wrote plays. He worked on the screen adaptation, Modesty Blaise, but his treatment was largely ignored in the final product. He continued writing Modesty Blaise stories until 2001, when he fully retired from writing, though he continued to occasionally contribute supplementary materials to various publications of his earlier work. As per his request, no further Modesty Blaise stories have been written by other authors.
Born and raised in England, O'Donnell fought in the Second World War as a young man. He and his wife Constance, whom he married in 1940, had two daughters. In his later years he suffered from Parkinson's Disease. He died on May 4th, 2010 at the age of 90.