At a young age he joined the Sports Club of Trikala. After completing his high school education he enrolled in the Sports Academy of Athens. While in Athens, he joined Panathinaikos.
It was Papanikolaou who broke the Greek record of Melbourne bronze medallist, Georgios Roubanis, in 1964. He would eventually take the Greek record from 4.60m to 5.49m. On August 7, 1967, he also broke the Greek record for the decathlon.
His greatest championship achievements came when he won the silver medal at the 1966 European Championships and finished fourth at the 1968 Summer Olympics. In finishing fourth in Mexico, Papanikolaou broke the Greek record with a 5.35m jump.
At the 1970 Universiade in Turin, Papanikolaou finished second behind Wolfgang Nordwig, who won the event with a new world record of 5.46 metres. On October 24 the same year Papanikolaou jumped 5.49 metres in Athens to capture the world record. Measuring 18′ 14″, it was the first pole vault over 18 feet. The record was later beaten by Swede Kjell Isaksson who achieved 5.51 metres on April 8, 1972.
Papanikolaou was ranked by Track and Field News among the top ten pole vaulters a total of seven times between 1966 and 1972, more than any other Greek athlete. His highest ranking position was second in 1970. 
|1966||European Championships||Budapest, Hungary||2nd|
|1967||Mediterranean Games||Tunis, Tunisia||1st||5.15 CR|
|1968||Olympic Games||Mexico City, Mexico||4th|
|1971||Mediterranean Games||Izmir, Turkey||1st||5.20 CR|
|1972||Olympic Games||Munich, West Germany||11th|