Papanikolaou began his professional career in 1992 with the Greek club
Sporting Athens when he was transferred from the amateur club Asteras Neon Liosion. He then transferred to
Olympiacos Piraeus in the year 1995. With Olympiacos, he won 2
Greek Basket League championships (1996, 1997), 2
Greek Cups (1997, 2002), the
EuroLeague championship (
1997), and also the
Triple Crown (1997). In 1997 summer Papanikolaou left Olympiakos for
Virtus Bologna, but he wasn't free for the Italian club until his 21st birthday. Finally, after 5 months without official action in
Bologna, he signed a new contract with Olympiacos. In 2002, he moved to
Makedonikos Kozani, and then in 2003, he moved to
Panathinaikos Athens. With Panathinaikos, they won 4
Greek Basket League championships (2004, 2005, 2006, 2007), 3
Greek Cups (2005, 2006, 2007), the
EuroLeague championship (
2007), and also the
Triple Crown (2007). In 2007, he moved to
AEK Athens, in 2009 to
Panionios, and a year later he joined
Peristeri. He announced his retirement from professional basketball on August 22, 2011.{{cite news|url=http://www.contra.gr/Basketball/Hellas/telos-to-mpasket-gia-ton-dhmhtrh-papanikolaoy.1337007.html ==National team career==