Mor Iyawannis became a monk and studied at the Monastery of Eusebuna or at Zuqnin (according to another source). He was ordained metropolitan of Hawran. And in 737 was chosen of three metropolitans by lot and elevated to the Holy See of Antioch. When the Caliph Marwan II, visited Harran, the patriarch Iwannis came to him with fifty camels carrying presents. The King greatly honored him and provided him with a decree of authorization.

Iwannis died in 754, a very aged man. In the late period of his life he wrote a Synodical letter to the bishops who assembled at Talla in 752, prescribing that it be announced in all the churches. This letter, which was incorporated by Michael the Great into his chronicle, exhibits the excellence of Iwannis, his humility and zeal for the Church, as well as his happiness because of the peace of the Church.