Born in Morden, Manitoba, he served articles first with a law firm in Morden, then moved to Winnipeg to finish his articles in the office of Albert Hudson, who was later appointed to the Supreme Court. Locke was called to the bar of Manitoba in 1910 but interrupted his legal practice to serve overseas with the Canadian military in World War I, being awarded the Military Cross. After the War, he returned to practise in Winnipeg, but in 1928 he moved to Vancouver, joining the bar of British Columbia.
Locke was appointed to the Supreme Court of Canada on June 3, 1947, filling the vacancy caused by the death of his mentor, Albert Hudson. He was the first person born in western Canada to be appointed to the Supreme Court. He served as Puisne Justice until September 16, 1962.