Saint Celestine was a native of Rome, a relative of the emperor Valentinian, and at the death of Pope Saint Boniface in September 422, he was chosen to succeed him, by the consent of the entire city.
His first official act was to confirm the condemnation of an African bishop who had been convicted of grave crimes. He wrote also to the bishops of the provinces of Vienne and Narbonne in Gaul to correct several abuses which had followed upon errors in doctrine. He stipulated, among other things, that absolution or reconciliation should never be refused to any dying sinner who sincerely asked it; for repentance depends not so much on time as on the heart, which can be changed in a moment when God so wills.
Saint Celestine assembled a synod at Rome in 430, by which the writings of Nestorius were examined, and the heresiarch's obstinate errors in maintaining in Christ two persons, a divine and a human, were condemned. The Pope pronounced sentence of excommunication against Nestorius, and deposed him. Being informed that in Great Britain, the seeds of the Pelagian heresy, denying the necessity of grace, were spreading, Saint Celestine sent there Saint Germanus of Auxerre, whose zeal and ministry happily prevented the threatening danger.
He also sent Saint Palladius, a Roman, to preach the Faith to the Scots, both in North Britain and in Ireland. Many authors of the life of Saint Patrick say that he, too, received his commission to preach to the Irish from Saint Celestine, in 431. This holy Pope died on the 1st of August, in 432, having reigned almost ten years.