Born on 11 April 1920 in Lewisham, London, O'Donnell was the son of Bernard O'Donnell, a journalist on the Empire News, and was educated at Catford Central School. He began to write professionally at the age of 16. In 1938 he joined the British Army, and during the war served as an NCO in mobile radio detachment of Royal Corps of Signals in the 8th Army. He saw active service in Persia in 1942, after which his unit was moved to Syria, Egypt, the Western Desert, and Italy, and he was with forces that went into Greece in October 1944. After the war, O'Donnell returned to civilian life and began to script comic strips, including an adaptation for the Daily Express of the James Bond novel, Dr. No. From 1953 to 1966 he wrote for Garth, and from 1956 to 1962 Romeo Brown. 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 he drew the strip until it ended in 2001. In 1965, O'Donnell novelized his screenplay for a motion picture version, which was published as Modesty Blaise. This book was a huge success and O'Donnell would publish a dozen more novels and short story collections until 1996. Kingsley Amis said the novels were "endlessly fascinating" and that Blaise and Garvin were "one of the great partnerships in fiction, bearing comparison with that of Sherlock Holmes and Dr Watson." At the request of publisher Ernest Hecht, he began writing gothic romance and adventure novels under the pen name of Madeleine Brent. The novels are not a series, but feature a variety of strong female protagonists. They are written in first person, take place in the late Victorian era, and although every protagonist has connections to England, part of each book is set in various locations around the world—including China, Australia, Afghanistan, and Mexico. In 2001, O'Donnell retired from writing the Modesty Blaise comic strip and was also said to have retired from full-time writing. From 2004 to 2009 he wrote the introductions for a series of Modesty Blaise comic strip reprint volumes published by Titan Books; beginning in 2010, just prior to O'Donnell's death, another writer had begun composing these introductions. He was also interviewed for a special feature included on the DVD release of the 2004 film My Name Is Modesty, which was based on his creation. O'Donnell's wish was that no one else write any future Modesty Blaise stories, but whether this was ever formalized is unknown. With the exception of "The Dark Angels" adaptation and the My Name is Modesty film, no further new productions related to the character have been released as of 2015. In 2007, working with young women students at Bullers Wood and Newstead Wood schools, he established an official website,
Death
According to his obituary in the Evening Standard, O'Donnell had been suffering from Parkinson's disease in his later years. He died at age 90 in Brighton, Sussex. Peter is buried in the same grave with his wife, Constance, at Lawn Memorial Cemetery, Warren Road, Woodingdean, Brighton, Sussex.
O'Donnell also wrote romance books and television and movie scripts. Mr. Fothergill's Murder first opened on 25 October 1982 at the Duke of York theatre, London, and was published by the English Theatre Guild. Among other places, it was performed at The English Theatre of Hamburg in the 1987-88 season.
