Demyanenko was a longtime Dynamo Kyiv captain and a prolific left-footed player for the Soviet Union who could patrol the entire flank from defence to offence. In December 2000 he was voted the 3rd best player in the Ukrainian 'Team of the Century' according to a poll by The Ukrainsky Futbol weekly, behind Andrei Shevchenko and Oleg Blokhin. Demyanenko is fourth in the all time caps records for the USSR and played in three World Cups for them.
Demyanenko started out his coaching career with FC CSKA Kyiv in 1993. After the Army men merged with FC Boryspil became a member of the coaching staff newly formed FC CSKA-Borysfen Kyiv. Already next season Demyanenko joined Dynamo Kyiv in 1994. Until 2005 he was a regular coach of the Dynamo's big coaching staff then he was offered to become the manager. During this time he won the Ukrainian Premier League once in 2006–07. He also won the Ukrainian Cups 2005–06, and 2006–07. Following several defeats of Dynamo Kyiv early on in the 2007–08 season, Demyanenko resigned coaching Dynamo in September 2007.
In January 2008, Demyanenko became the coach of Neftchi Baku in Azerbaijan, following the sacking of their coach Vlastimil Petržela. Demyanenko made history in Azerbaijan, making Neftchi become the first club that managed to get to the third round of UEFA Cup Qualification. However, he was sacked after the Azerbaijan Premier League started and he lost the first two games.