 He was born in 1942 and began his career at Nea Genea in the town of Nea Nikomedia (now a part of Veria), Imathia.He joined AEK in time for the 1963 season for the paltry sum of 140,000 drachmas.Papaioannou proved an instant success helping AEK win their first post-World War II title, scoring twice in the final playoff game of the season against Panathinaikos FC.