Jonas Čepulis never won a Soviet title, but won silvers at the Soviet Championships in 1965 and 1968 and bronze in 1966. At his only international tournament, at the 1968 Olympics, Čepulis won a silver medal, losing in the final to the famous American George Foreman by TKO. Čepulis had defeated his previous three opponents at the Olympics by TKO. Čepulis was also six times Lithuanian SSR champion (1963-1964, 1966-1967 and 1969-1970) and won the Baltic Championships in 1962. In all Čepulis retired from boxing with a record of 203 wins out of 230 bouts. After retiring from sports, Čepulis worked in a Pergalės factory in Kaunas.