He was ordained a priest in Rome and earned doctoral degrees in these disciplines, becoming one of the first Indian nationals to achieve this distinction in the 18th century.

Working closely with prominent lay leader Thachil Mathu Tharakan, Kariattil supported the efforts of Francis De Sales, the Apostolic Vicar of Varapuzha, to settle in Alangad Church in 1776.

[citation needed] In 1778, Kariattil embarked on a significant journey to Rome with Paremmakkal Thoma Kathanar to present the issue of unification to church authorities.

Impressed by his humility, intellect, and religious dedication, the Queen appointed Kariattil as the Archbishop of Kodungalloor (Cranganore) on 16 July 1782, in Lisbon.

Pope Pius VI later confirmed his appointment, making Kariattil the first native Indian Archbishop of the Archdiocese of Kodungalloor.