Educated at St Paul's Cathedral School. He is credited with breaking the power of the notorious Glasgow razor gangs during the 1930s, made infamous in the novel No Mean City. He was Chief Constable of the city's police force from 1931–43, having previously undertaken the same role in Sheffield, and went on to head MI5. During his time as Chief Constable of City of Glasgow Police, he was credited with the introduction of wireless radios allowing communication between headquarters and vehicles, which previously relied completely upon the use of Police boxes, use of civilians in police related roles, and the introduction of compulsory retirement after 30 years service.
He is further credited with the introduction of the Sillitoe Tartan which is more commonly recognized as the black and white diced pattern on police cap bands, originally based on that used by several Scottish regiments on the Glengarry. His reputation was damaged by the 1951 defection to the Soviet Union of the spies Guy Burgess and Donald Duart Maclean, and by the investigation afterwards, which showed that MI5 had been unaware and slow to act.