István represented Hungary as a Water polo player 96 times and was a member of teams that won the silver medal at 1972 Munich Olympics, the gold medal at the 1973 World Championships, the silver medal at the 1975 World Championships. From 1984 to 1990, he was Head Coach of Ujpest in the Hungarian National League, leading them to a championship in 1986. From 1991 to 1994, he was Head Coach of CACEL Nice Water Polo Club in the French National League, winning the championship 3 times.
He then moved to Australia and in 1998, was appointed the Australian women’s national water polo team Head Coach. That team went on to win the inaugural water polo gold medal at the 2000 Sydney Olympics.