Viktor Demyanenko won his first Soviet Championship medal, a silver in featherweight, in 1978. The next year, Demyanenko switched to lightweight, and won his first Soviet title and also won gold at the European Championships and the World Cup. In 1980 Demyanenko won his second Soviet title, but at the Olympic Games, lost unexpectedly to Cuban Angel Herrera by TKO in the final and had to settle for a silver. At the 1983 European Championships Demyanenko took bronze, losing to Bulgarian Emil Chuprenski in the semi-final and took his last Soviet title in 1983. In 1984, Demyanenko won his last medal, a bronze, at the Soviet Championships and retired from boxing after that with a record of 267 wins out of 290 bouts. Later Demyanenko worked as a president of the Kazakhstan Boxing Federation.