Percy Sillitoe was born in 1888. he joined the British police force in South Africa in 1908. Three years later he moved to the Northern Rhodesian Police in 1911 and during the First World War served in the German East African campaign.
On his return to England he joined the police force and eventually became Chief Constable of Sheffield. In 1929 he established Britain's first forensic science laboratory. As Chief Constable of Glasgow he developed a reputation as an effective gang-buster. After the Second World War he served as Chief Constable of Kent.
In May 1946 Sillitoe replaced David Petrie as head of MI5. Guy Liddell was expected to succeed David Petrie as chief of MI5. However, Ellen Wilkinson, who served under Herbert Morrison, the Home Secretary, had heard rumours from Europe that Liddell was suspected of being a double-agent. As a result, Liddell did not get the top job and instead became Deputy-Director-General.
During his period of office Sillitoe had to deal with the problems of Soviet spies such as Kim Philby, Guy Burgess, Donald Maclean and Anthony Blunt. Sillitoe eventually retired in 1953 and was replaced by Sir Dick White. After his retirement Sillitoe worked for the De Beers company in South Africa.
Sir Percy Sillitoe died in 1962.