La Fontaine was originally born at Eskdale, in north-eastern Victoria (Australia). While still a youngster his parents Cyrelle and Beatrice brought the family to Melbourne where they settled in the suburb of Footscray. He had three brothers, Claude, Lionel and Donald. La Fontaine attended St. Joseph's CBC North Melbourne (later St. Joseph's College Melbourne) from 1925 to 1929 where he earned the title Captain of College for 1927, 1928 and 1929. He went on to complete his secondary education at St Kevin's College, Melbourne before proceeding to university where he eventually gained a Bachelor of Science.
During the second world war, La Fontaine served as a Flying Officer with the RAAF between 1942 and 1945 and on his return took up his trade as an industrial chemist. Two of his brothers served in the Australian Army during the same conflict.
La Fontaine's football career changed dramatically when he was recruited from University Blacks. He was considered a brilliant full-forward, and was to earn his fame playing with the Melbourne Football Club as a centreman. He was captain of Melbourne during their hat-trick of premierships in 1939, 1940 and 1941. La Fontaine went on to coach Melbourne from 1949 until 1951.