In 1916, Keeper joined the Army, and served for two years in France. He received The Military Medal for his actions at Cambrai during WWI. In 1917, Keeper joined with Tom Longboat to win an inter-Allied cross country championship near Vimy Ridge. Longboat, Keeper, and other First Nation long-distance runners A. Jamieson and John Nackaway served as dispatch carriers for the 107th Pioneer Battalion. In addition to the Military Medal, Keeper received the British War Medal and the Victory Medal.