Sir Stewart Graham Menzies (January 30, 1890 - May 29, 1968) was the Chief of MI6, British Secret Intelligence Service, during and after the World War II.

Stewart Graham Menzies was born in London into a wealthy family. He has also been reputed to be the illegitimate son of future King Edward VII.

Menzies joined the Royal Military Academy Sandhurst and later joined the Grenadier Guards. During the World War I he served in France, was seriously injured in a gas attack in 1915 and was honorably discharged. He joined the counterintelligence section of Field Marshall Douglas Haig. He entered MI6 (later SIS) and became a deputy of its director-general David Sinclair .

When Admiral Sinclair died in 1939, Menzies was appointed the Chief of SIS. He expanded wartime intelligence and counterintelligence departments and supervised cryptographic efforts of Bletchley Park. He also supported efforts to contact anti-Nazi resistance , including Wilhelm Canaris, the anti-Nazi head of Abwehr, in Germany but failed to convince Winston Churchill. He also coordinated operations with SOE (although he reputedly considered them "amateurs"), OSS and the Free French Forces.

After the war, Menzies reorganized the SIS for the Cold War. He absorbed most of SOE. He was sometimes at odds with the Labour governments. He also had to weather a scandal inside SIS after revelations that SIS officers Guy Burgess, Donald Maclean, and, eventually, Kim Philby, were actually Soviet spies.

Menzies resigned in 1952 and retired to rural Gloucestershire.