Son of Owen Leonard and Annie Leonard (nee Daley); older brother of Captain Leonard Dennis Dakey 'Leo' Leonard (C.A.D.C.)
He was a graduate of the Medical Class of 1911 at Toronto University.
The Hospital Ship Llandovery Castle, bound from Halifax, Nova Scotia, for Liverpool, was torpedoed on June 27th, 1918, 114 miles south-west of the Fastnet Rock by U-86. Despite regulation Red Cross lights, the ship was deliberatly torpedeod and most survivors, including 14 Nursing Sisters were machine gunned. The Llandovery Castle became the rallying cry for the Canadian troops during the Last 100 Days offensive.
In August 1915 he was appointed to the C.A.M.C., and served for a month at Niagara Camp before going overseas. He crossed to France in November 1915 and was attached as Medical Officer to the 2nd Brigade, Canadian Field Artillery, later joining No. 2 Field Ambulance. He took part in the battles of Somme, Vimy, and Hill 70. In November 1717 he returned to England and joined the staff at No. 16 Canadian General Hospital at Orpington. In December of the same year he was attached to the Hospital ship service, first with H.M.H.S. 'Araguaya', and later, in March 1918, with H.M.H.S. 'Llandovery Castle'. He was drowned at sea when this ship was sunk by an enemy submarine.