Stefanos Athanasiadis began in his birthplace Lakkoma with the football game. In 1996, he joined the youth of PAOK Thessaloniki. Two years later moved with his family to Athanasiadis to Trieste and played for a short time in the U.S. Triestina. After a month in Trieste he went to relatives in Berlin. There Stefanos Athanasiadis completed workouts at Hertha BSC, before he returned to PAOK Thessaloniki partly because of language problems in September 1998. In summer 2006, he signed his first professional contract there. On February 24, 2007 debuted with Athanasiadis PAOK Thessaloniki against AE Larisa in the Super League. In the 2009/10 season Stefanos Athanasiadis played on loan for Panserraikos in the Beta Ethniki, reaching with his Leihverein about the playoffs promotion to the Super League.
Athanasiadis debuted for the national team of Greece on 8 June 2011 in a friendly against Ecuador. On October 11, 2011 Stefanos Athanasiadis graduated in qualifying for the European Championship 2012 for Greece against Georgia his first senior international match Mandatory.