In 1911, he joined the Home Office as a civil servant, where he worked in various capacities including Secretary to the Labour Resettlement Committee (1918–1919) and Chairman of the Prison Commission (1932–1939).

With the outbreak of the Second World War, Scott's work took on a more military capacity, as he joined London's Civil Defence Administration until he was appointed as Permanent Secretary of the Ministry of Aircraft Production in 1943.

In late 1944, the Home Secretary Herbert Morrison asked Scott to accept the post as Metropolitan Police Commissioner when the war was over.

He also improved the public relations outlook of the service, including granting Ealing Studios unprecedented assistance in the production of the film The Blue Lamp, which was to lead to the TV series Dixon of Dock Green, which painted a rosy view of the Metropolitan Police fostered by Jack Warner's portrayal of genial PC George Dixon.

Scott presided over several high-profile cases during his time with the Met, including the Derek Bentley trial for the murder of police officer PC Sidney Miles.