Stuart Belknap was born in Syracuse, New York, but later lived in Keene, not far from Lake Placid. He was with the Army in World War I as a private first class with the 310th field artillery battery, serving from 14 July 1918 to 26 May 1919. After the war he became a mechanic at a shipyard in New York City but Belknap later became a machinist who worked in Washington, DC for the US Navy. He eventually settled in Napa, California, and was buried in Golden Gate National Cemetery in San Bruno, California.