Ambrosios was born on March 15, 1960 on the island of Aegina in Greece where he graduated from high School in 1978. In 1983 he received his degree from the School of Theology of the University of Athens. In 1985 he was ordained deacon and in 1991 presbyter. As a deacon and priest he served at the Metropolis of Nicea-Piraeus as Personal Secretary of the late Metropolitan Georgios (Pavlides) of Nicea and as Youth Director. He also served at the Metropolis of Monemvasia and Sparta.