Gavin Tudor Lyall (May 9, 1932 - January 18, 2003) was a English author of espionage thrillers. Lyall won the British Crime Writers' Association's Silver Dagger award in both 1964 and 1965.

Up to the publication in 1975 of Judas Country, Lyall's work falls into two groups. The aviation thrillers (The Wrong Side Of The Sky, The Most Dangerous Game, Shooting Script, and Judas Country), and what might be called "Euro-thrillers" revolving around international crime in Europe (Midnight Plus One, Venus With Pistol, and Blame The Dead). All these books were written in the first person, with a sardonic style reminiscent of the "hard-boiled private-eye" genre. Despite the commercial success of his work, Lyall began to feel that he was falling into a predicable pattern, and abandoned both his earlier genres, and the first-person narrative, for his “Harry Maxim" series of espionage thrillers beginning with The Secret Servant published in 1980. This book, originally developed for a proposed BBC TV Series, featured Major Harry Maxim, an SAS officer assigned as a security adviser to 10 Downing Street, and was followed by three sequels with the same central cast of characters. In the 1990s Lyall changed literary direction once again, and wrote four semi-historical thrillers about the fledgling British secret service in the years leading up to World War I.