Born in London, England in 1889, the son of a clergyman. Was educated in Surrey and graduated from Charterhouse in 1909. Continued his education at St. Petersburg, Russia, where he studied music at the prestigious observatory and later worked as the assistant to the conductor of the Imperial Marinsky Opera. Took a job in 1916 with the Anglo-Russian Commission, reporting on the Russian press. The Anglo-Russian Commission coordinated the war efforts of the two countries during World War I.
Began working for the British government as a spy in 1918 and met with MI6 head Mansfield Cummings. Was given a brief training in espionage but was hurriedly sent to Russia where he monitored the turbulent activities surround the Russian Revolution and the rise of the Bolshevik party. He employed any number of disguises and covers as he worked from deep within, assessing the strength of the fragile, new Bolshevik government. He recommended the the British government support the White Russians, a group opposing the Bolshevik regimes and working towards its overthrow. Dukes went so far as to row in a small boat into the Baltic Sea where he met with British patrol ships.
Was made a spymaster within Russia, working with the National Center, an organization representing the White Russians. Dukes helped to finance this group and its soldiers with money received from Britain (although much of the money he received from England was counterfeit).
Worked on behalf of MI1c, a branch of the British intelligence system, aimed at rescuing political or military refugees. He set up elaborate plans to aid prominent White Russians to escape from Russian prisons and helped hundred of them escape to Finland. Worked alongside Naval Lieutenant Augustus Agar, a torpedo motorboat squadron leader. Dukes would pass on information about Russian warship deployment and Agar would use this as a guide to leading an torpedo assault on the squadron).
Dukes continued his use of disguises, which aided him in assuming a number of identities and gained him access to numerous Russian organizations. He joined (among others) the Communist Party , the Comintern, and the Russian secret police, the Cheka. He learned of the inner working of the top Russian leaders, and passed along their plans to British intelligence authorities and well as on troop movement and battle plans.
Was forced to flee Russia after N.N. Schepkin (the head of the National Center) and almost 70 White Russians were captured and executed in 1919. He was successful in evading the Cheka, traveling through long, brutal stretches of land until he ended up in Latvia. He recounted his adventurous escape to friendly White Russian, but was exposed when someone recounted these stories to the Latvian press. As such, he was unable to return to Russia.
Returned to Britain a distinguished hero, and in 1920 was knighted by King George who called Dukes the "greatest of all soldier). Dukes was, at the time, the only person knighted based entirely on his exploits as a spy. Briefly returned to service in 1939, helping to locate a prominent Czech business who disappeared after the Nazi occupation of Czechoslovakia.
Died in 1967.