Niniadis was born on February 18, 1971, in Georgia. He started his football career in Georgia, migrating to Greece after the breakup of the Soviet Union. He was a player of Pontioi Veria from 1991 until 1994 when he transferred to Ethnikos Piraeus. In the summer of 1996, he was acquired by Olympiakos.
He presently works as a scout for Olympiakos.