Julian Symons was born in London. He was a younger brother, and later the biographer, of the writer A. J. A. Symons.
He left school at 14. He founded the poetry magazine Twentieth Century Verse in 1937, editing it for two years. "He turned to crime writing in a light–hearted way before the war and soon afterwards established himself as a leading exponent of it, though his use of irony to show the violence behind the respectable masks of society place many of his books on the level of the orthodox novel." In World War II he applied for recognition as an anti-capitalist conscientious objector, but ended up in the Royal Armoured Corps 1942 to 1944, when he was invalided out with a non-battle-related arm injury. After a period as an advertising copywriter, he became a full-time writer in 1947. During his career he won two Edgar Awards from the Mystery Writers of America and, in 1982, received the MWA's Grand Master Award. Symons served as the president of the Detection Club from 1976 till 1985.
Symons's 1972 book Bloody Murder: From the Detective Story to the Crime Novel (published as Mortal Consequences in the US) is one of the best-known critical works in the field of crime fiction. Revised editions were published in 1985 and 1992. Symons highlighted the distinction between the classic puzzler mystery, associated with such writers as Agatha Christie and John Dickson Carr, and the more modern "crime novel," which puts emphasis on psychology and motivation.
Symons published over thirty crime novels and story collections between 1945 and 1994. His works combined elements of both the detective story and the crime novel, but leaned clearly toward the latter, with an emphasis on character and psychology which anticipated current crime fiction writers such as Ruth Rendell and P.D. James. His novels tend to focus on ordinary people drawn into a murderous chain of events; the intricate plots are often spiced with black humour. Novels typical of his style include The Colour of Murder (1957), the Edgar-winning The Progress of a Crime (1960), The Man Whose Dreams Came True (1968) The Man Who Lost His Wife (1970) and The Plot Against Roger Ryder (1973). Symons's crime fiction is highly prized by connoisseurs, even if it is less well-known to the general reading public.
Symons wrote two modern-day Sherlock Holmes pastiches, as well as a pastiche that was set in the 1920s. In A Three Pipe Problem (1975), the detective was "...a television actor, Sheridan Hayes, who wears the mask of Sherlock Holmes and assumes his character. The book neatly reversed the usual theme of the criminal behind the mask by having a rather commonplace man wearing the mask of the great detective." The Kentish Manor Murders was written in 1988. For his 1981 book The Great Detectives, he wrote a Sherlock Holmes pastiche instead of a biographical sketch. Entitled "How a Hermit was Disturbed in His Retirement," the events of the tale take place in the 1920s as Sherlock Holmes is drawn out of retirement in order to solve an unusual missing persons case. The story was included in the collection The Further Adventures of Sherlock Holmes, in which it was given a more Doylean title of "The Adventure of Hillerman Hall." He also made occasional forays into historical mystery, such as The Blackheath Poisonings (1978), which was filmed for television in 1992.