Born in Canada, Hartney worked as a clerk in his brother's law firm in Saskatoon after graduating from Toronto University in 1911. After obtaining a graduate degree from the University of Saskatchewan, he became a barrister, joined the Saskatoon 105th Fusiliers, and played the cornet in the town's band. Married in 1914, he shipped out for England with the Canadian Expeditionary Force less than a year latter. As he trained with his battalion on Dibgate Plains, Hartney's visit to an aerodrome near Folkstone and a chance meeting with William Bishop led to his request for transfer to the Royal Flying Corps. On October 21, 1915, Hartney entered the RFC at Norwich. The following day, he survived a near fatal first flight in a Maurice Farman longhorn. By the following year he was grasping the stick of an F.E.2, flying reconnaissance missions over the Western Front. After scoring 5 confirmed victories, he was shot down for the fourth time by Manfred von Richthofen on the afternoon of February 14, 1917. On September 21, 1917, Hartney was promoted to Major and ordered back to Toronto to assume command of the American 27th Aero Squadron. As a member of the United States Air Service,  he scored two more victories by the end of the war. In 1923, Hartney became a citizen of the United States and published an autobiography, "Up and at 'Em," in 1940.

Distinguished Service Cross (DSC)
"For extraordinary heroism in action near Fismes, France, August 13, 1918. Major Hartney voluntarily accompanied a reconnaissance patrol. Realizing the importance of the mission, Major Hartney took command and although five enemy planes repeatedly made attempts to drive them back, he continued into enemy territory, returning later to our lines with important information. The cool judgement and determination displayed by Major Hartney furnished an inspiration to all the members of his command." DSC