Leonard turned professional in 1938. He won the Canadian Professional Golfers' Association championship 8 times 1940-61, was low Canadian in the Canadian Open 9 times 1945-61, won the BC Open 5 times, the Alberta Open 9 times, and the Saskatchewan Open twice. Until 1955 Leonard's competitive golf was restricted to Canada. Then over 40, he began to compete on the US tour. In 1957 he won the Greater Greensboro (NC) Open, in 1958 the Tournament of Champions and in 1960 the Western Open.