Sir Percy Silitoe (1888–1962) came from a police background, like his predecessor Sir David Petrie. He served as Chief Constable of a number of police forces including Kent, Glasgow and Sheffield. He became the Security Service's Director-General in 1946.

During his time in office, Sir Percy faced the challenge of the post-war rise in Soviet and Communist spying and subversion in the UK. This included the exposure of the Cambridge spy ring and the "atom spies". He served as Director General until 1953. In 1955 he became the first former DG to publish an autobiography, Cloak without Dagger.

Following his retirement from the Service, Sir Percy became the head of the International Diamond Security Organization. He successfully stopped the smuggling of diamonds from Sierra Leone.