On the death of his father, John was made chief councillor of Damascus, which was around the same time that iconoclasm began to appear. John wrote against the Emporer's edict against icons, with three Apologetic Treatises against those Decrying the Holy Images, works that made his reputation. After a forged letter was sent by Leo the Isaurian, John's hand was cut off, but was restored after fervent prayer before an icon of the Virgin Mary.
The caliph, convinced of his innocence, wished to reinstate him, but John then retired to the Monastery of Saint Sabbas near Jerusalem, where he produced a stream of commentaries, hymns and apologetic writings, including the Oktoechos (the Church's service book of eight tones) and An Exact Exposition of the Orthodox Faith, a summary of the dogmatic writings of the Early Church Fathers. He died in 749 as a revered Father of the Church, with his feast celebrated on December 4.