On 30th October 1978, in response to the vast geographical expanse of its three outside Kerala dioceses, the Malankara Orthodox Church undertook a significant reorganization transforming them into five dioceses. This decision, approved by the Episcopal Synod, led to the establishment of the Calcutta Diocese, which came into effect on 1st January 1979. This restructuring aimed to ensure better pastoral care and administrative efficiency across the large regions under the Church’s jurisdiction.

The Calcutta Diocese, initially encompassing the states of Assam, Bihar, Madhya Pradesh, Manipur, Meghalaya, Nagaland, Orissa, Tripura, West Bengal, Mizoram, Arunachal Pradesh, and Nagpur in Maharashtra, also included parishes in Kuwait and Muscat, extending its reach across both India and beyond. This vast area was entrusted to the leadership of H.G. Dr. Stephanos Mar Theodosius, who became its first Metropolitan. Under his guidance, the diocese flourished, serving as a beacon of faith and mission to the poor until his passing on 5th November 2007. Following his demise, His Holiness the Catholicos assumed direct responsibility for the diocese, nominating H. G. Geevarghese Mar Coorilos of Bombay Diocese to assist in its administration.

In March 2009, H. G. Dr. Joseph Mar Dionysius succeeded as the Metropolitan of the Calcutta Diocese, continuing its spiritual journey. However, as the Church continued to evolve, it decided to further reorganize the outside Kerala dioceses into nine dicoeses. This led to the transfer of parishes in the Malwa region of Madhya Pradesh and Muscat in the Gulf region from Calcutta Diocese to the newly established Ahmedabad Diocese.

On 3rd November 2022, following the directive of His Holiness Moran Mar Baselios Marthoma Mathews III, H. G. Alexios Mar Eusebius took over as the Metropolitan of the Calcutta Diocese, ushering in a new chapter of leadership and spiritual growth for the faithful under his care. With a rich history of devotion and mission to the poor, the Calcutta Diocese remains a testament to the resilience and strength of the Malankara Orthodox Syrian Church as it continues to grow and serve the diaspora community.