Meletius had the tough assignment to be patriarch of Antioch during the early days of the Arian heresy. The question was about the divinity of Jesus: was he in fact one in being with the Father (Homoousianism) or was he a creature of the Father, and thus less divine in some way (Arianism)? Since the Council of Nicea, orthodoxy had declared that he was an eternal person of the Trinity, God from God, light from light, etc from etc. Meletius was a brilliant theologian who could argue with the best of them, but the Emperor Valens (though considerably less brilliant) had an army with really pointy spears. Meletius was wise enough not to take those points by taking exile instead, and eventually returning to his cathedral when Valens died.
Meletius presided over one and a half ecumenical councils in Antioch, at which the Eastern and Western churches were momentarily reconciled. They had not actually suffered a formal schism at that point, but the fault line was evident to everyone involved. Meletius was dedicated to patching the rift before it split wide open; he gave up the ghost during the second council and is thus canonized in both the Eastern and Western churches.