Prior to that, he served as Metropolitan of India, from 1952 to 1964, within the Church of the East.

[4] In June 1952, he was assigned as Metropolitan of India, based at Trichur (Kerala), and thus became one of senior hierarchs of the Church of the East.

In January 1964, he was suspended from the metropolitan office by Patriarch Shimun XXI Eshai.

[5][6] Subsequently, after three years of the seat of the Ancient Church of the East remaining vacant (1964–1967), Mar Thoma Darmo was elected as Catholicos-Patriarch in October 1968.

In 1995, under new Patriarch Dinkha IV of the rival Assyrian Church of the East, reconciliation between fractions in India was achieved, and on that occasion the validity of ordinations performed by Thoma Darmo after the suspension of 1964 was recognized, and in 1997 the suspension itself was annulled by the Holy Synod of the Assyrian Church of the East.