When the war began, Guyou was serving in the cavalry. In April 1915, he transferred to the French Air Service, receiving his Pilot's Brevet on 17 February 1916. After serving with N49, he was reassigned to N15 but was badly wounded on 23 September 1916. Returning to duty on 20 December 1916, he served briefly with three escadrilles before being pemanently assigned to N93 on 25 August 1917. By the end of the war, Guyou had logged 431 hours and 10 minutes of flight time against the enemy. After working as a commercial airline pilot, he rejoined the military during World War II.