The boundaries of the Thalassery ecclesiastical province were extended to include Mangalore, Chickmangalore, Mysore, Shimoga and Ootty as there were settlers in the neighbouring States.

[2] The ecclesiastical province came into existence on 31 December 1953 through the papal bull Ad Christi Ecclesiam Regendam issued by Pope Pius XII.

Later, as Syro-Malabar Catholics migrated even to the states of Karnataka and Tamil Nadu, the boundaries were extended to the present Latin Diocese of Mangalore, Chickmangalur, Mysore, Shimoga, and Ootacamund by a decree of the Holy See on April 29, 1955.

Petitions were sent to the Holy See by the bishops of the settlers, who had migrated to the British Malabar since 1930, requesting for a diocese of their own.

Cardinal Tisserant, the Prefect of the Oriental Congregation came to Malabar and personally saw the pitiable situation of the settlers.