Son of John and Wilhelmina Uyen (nee Steenaart), of London, ON. Youngest brother of Jo (Lavoie), Mientje (sister Canisius) and John (Monseigneur John Uyen). William and his siblings were born in Utrecht Holland, but moved to London ON when William was an infant.
Fluent in Dutch, William completed a two-year Arts course at the University of Western Ontario before enlisting. He was also an avid tennis player. He loved to build model airplanes, which would greatly influence his military career. At the time of his enlistment, William was working as a stenographer and clerk at the Canadian National Railway. He enlisted at Hamilton, ON with the 78 (R.A.F.) Sqdn in November 1941.
During the final days of the Air Battle over Berlin, Flying Officer Uyen was reported missing along with more than 8,000 other airmen. He was later presumed to have been killed.