Tappouni was reassigned as Titular Bishop of Batnae dei Siri on 19 January 1913, which was the same date he received his episcopal consecration from Patriarch Ignatius Ephrem II Rahmani.

Many people attempted to interfere and negotiate for Tappouni's release, including Emperor Franz Joseph of Austria.

On 24 June Tappouni was unanimously chosen by the Syrian Synod to replace the late Rahmani as Patriarch of Antioch, the leader of the Syriac Catholic Church.

Tappouni, who took the name Ignatius Gabriel, was the first Eastern Rite prelate to enter the College of Cardinals since 1895.

Theologically conservative, Tappouni urged Cardinal Giuseppe Siri to put forward his candidacy at the conclave of 1963.