The Diocese of Alleppey was erected by the Papal Bull "Ea Redemptoris Verba" of Pope Pius XII, dated June 19, 1952, which divided the northern territory of the old Cochin Diocese at the Kuthiathodu Canal Line. The territory to the north of that line belongs to the Cochin Diocese and that to the south of it, to the Diocese of Alleppey.

The executorial Decree of September 8, 1952 assigned to each of the Diocese of Alleppey and Cochin a supplementary personal jurisdiction over certain parishes in the territory of the other. This Decree was approved by the Sacred Congregation for the Propagation of Faith on September 24, 1952 and became effective on October 11, 1952.

The boundaries are: on the north, the Kuthiathodu Canal Line; on the south, a straight line from the curve of the Pampa River at Viyapuram to the Arabian Sea through Thottappally; on the east, a line along the middle of the Vembanadu Lake continued to the south by the Pallathuruthy Canal, one of the main branches of the Pampa River, to Viyapuram; on the west: the Arabian Sea.

The area assigned to the Diocese comprises roughly the area of the Jesuit Mission of St. Andre of Muterte.