He was born in Ingersoll, Ontario. Despite his father's death while he was still young, Clark was able to complete his education at the local high school and went on to attend Victoria College. In 1914, he began the study of law at Osgoode Hall. During World War I, he served with the 96th Lake Superior Battalion and saw action at the Somme, Vimy, Passchendaele, Canal du Nord and Valenciennes. He resumed his legal studies in 1919, articled in Port Arthur, was called to the Ontario bar in 1920 and entered practice in Windsor. In 1930, Clark travelled to England to successfully argue a case before the British Privy Council.