Giannakopoulos was born in Kallithea in 1941. He was the son of Antonis Giannakopoulos, a former Panionios player. He started his career at Ethnikos Koukaki before moving to Panionios in 1958. In 1963, he moved on to Panathinaikos where he was sparingly used.
Giannakopoulos ended his career at Kallithea FC. Afterwards, he coached minor clubs such as Phoenix Kallithea and Moschato FC.