The History of the new Dharmapuri diocese is closely connected with that of Salem from where the diocese was bifurcated in 1997. In the year 1623, Christianity came into existence in the Diocese of Salem through the famous Jesuit Fr Robert De Nobili, his successors and later on through the Portugese Jesuits of Madurai Missions. In 1654 the Italian Jesuits of Mysore had their residence at Dharmapuri and began to preach the Gospel in the region as far as Tirupattur in North Arcot district. In 1674, St. John De Britto, visited Dharmapuri on his way to Kolei. He stayed at Dharmapuri with his Confreres, being accompanied by Fr Antony Ribero. In 1687, the Mysore Church work began to spread and preach the Gospel in the present districts of Salem and Dharmapuri. Inspite of the Pombal decree, suppressing the Jesuits, they carried on working under the jurisdiction of Cranganore. In 1711, Fr De. Cunha, a Father was killed by the local people as he was on his horse back towards the Church work place, near Hosur.

In 1776, the Holy Father handed the Madurai Missions and the Malabar Missions to the care of the M.E.P. Fathers. In 1785, Msgr Chapenois, mep. Superior of Malabar Mission was given the responsibility by Rome to look after the entire Mysore Mission, of which the old Diocese of Salem formed a part. In 1794, he was the first Bishop to visit the Diocese of Salem and left there Abbe Dubois, mep who tried to bring up the Church work. This region continued to depend on Coramandal Missions, and later, on the Apostolic Vicariate of Pondicherry, which became an Archdiocese in 1886. This set up continued till 1930 except for Hosur Taluk, which had been entrusted from 1861 to the care of the Mysore Missions. On August 3, 1930, the Diocese of Salem was erected.

Because of the vastness of the Diocese of Salem, the district of Dharmapuri was separated and declared a diocese by the Holy Father Pope John Paul II on January 24, 1997. Msgr Joseph Antony Irudayaraj, sdb, a Salesian was appointed as its First Bishop. This diocese is the 15th diocese of the Tamil Nadu region.