Georgios Papasideris studied and practiced law in the municipality of Kropia in Attica where he also donated his property for public benefit projects. Described as a model athlete, Papasideris competed in the shot put, discus throw, and weightlifting. Just prior to the 1896 Athína Olympics he finished in second place in weightlifting at the Panhellenic Games, which were used as qualification for the Olympics.
At the Athína Games Papasideris finished in joint-fourth place in the two-handed weightlifting event, tying with the German Carl Schuhmann, after they both lifted 90kg. Papasideris had better success in the shot put when he threw 10.36 metres to win the bronze medal. He also competed in the discus throw but his distance was not recorded. In 2015 the handball club GS Papasideris was founded in his honour.