Grew up in Hungary and was a noted coxswain in that country. At the 1948 Olympics he coxed Antal Szendey and Béla Zsitnik to a bronze medal in the pairs, and coxed the Hungarian eight at the 1952 Olympics. He would have been on the 1956 Olympic team, but when the Russians invaded Hungary that country sent only a few competitors to Melbourne. Shortly after that episode, Zimonyi defected to the United States and joined the Vesper Boat Club as a coxswain. When he became a U.S. citizen he was eligible to compete for the USA team and, in addition to his Olympic gold medal, he won two gold medals at the Pan-American Games and coxed numerous Vesper crews to national championships.