Simla-Chandigarh Diocese has a long history. The Archdiocese of Simla was created in 1910 when it was separated from the Archdiocese of Agra, the mother Diocese of all North India. Very Rev. Fr. Anselm E.J. Keneally O.F.M. Cap., Superior General of the Friars Minor Capuchins was appointed as the first Archbishop of this new Archdiocese, and he was consecrated in Rome on 1st January 1911. The Church of St. Michael and St. Joseph in Simla built in 1885 by Lord Ripon, the Catholic Viceroy of India, became the Cathedral of new Archdiocese.

The century of history of this Archdiocese witnessed great changes and has been affected by the changed political and ecclesiastical history of the country as a whole. The greatest of these was the partition and Independence of the country, to form the new Diocese of Lahore in Pakistan. The realignment of the states, the creation of the new city of Chandigarh and its Union Territory status have all influenced the history of the Diocese and have had their effect in the structure and development of the Diocese.

When the political capital of the country was shifted to Delhi, the Catholic population was placed under the jurisdiction of the Diocese of Simla thus becoming the Delhi-Simla Archdiocese and the See shifting to Delhi. Archbishop Sylvester P. Mulligan was the first Archbishop of Delhi-Simla Archdiocese, which comprised of the present states of Himachal Pradesh, Punjab, Haryana, Delhi and the Union-Territory of Chandigarh. Archbishop Sylvester P. Mulligan was succeeded by Archbishop Joseph Alexander Fernandes. In 1959, the Archdiocese of Delhi-Simla was dismembered to form Simla as an independent Diocese and thus beginning the history of the current Diocese with Bishop John Burke as its pastor.

In the year 1966, Bishop John Burke was succeeded by Bishop Alfred Fernandes, the Vicar General of Archdiocese of Hyderabad. He was transferred to the See of Allahabad in 1970. After the transfer of Bishop Alfred Fernandes in 1970, the Holy See appointed Bishop Gilbert B. Rego to be the Bishop of Simla in 1971. Initially Bishop stayed in Simla. In the course of his pastoral travel around the Diocese, he saw the foundation of the new city of Chandigarh gave rise to a new concept of urban Punjab and the political and social life of people began to shift and centre around the new city. Even though the bishop kept Simla as the headquarter of the Diocese, he was forced to remain in Chandigarh to be closer to the people and their lives till finally Bishop Gilbert B. Rego shifted the residence to Chandigarh and the Diocese came to be known as Simla-Chandigarh Diocese.

The present Diocese of Simla-Chandigarh has a total area of 83,560 sq. km. and is spread in states of Himachal Pradesh, Punjab and Haryana.

The Diocese of Simla-Chandigarh consists of:

• 1: 8 civil districts in Himachal Pradesh: Kinnaur, Lahaul-Spiti, Kullu, Mandi, Bilaspur, Simla, Solan and Sirmour;
• 2: 12 civil districts in Haryana: Panchkula, Ambala, Yamunanagar, Kurukshetra, Karnal, Panipat, Kaithal, Jind, Hissar, Bhiwani, Fatehbad and Sirsa;
• 3: 8 Districts in Punjab: Barnala, Mohali, Patiala, Sangrur, Mansa, Bhatinda, Fatehgarh Sahib and Ropar; and the Union Territory of Chandigarh.
• 4: This vast area accounts for a population of about 5,39,51,800 of which only 20,750 are Catholics. There are pockets of other Christian denominations too. The area is the home of Sikhism and the other great religions of India, Hinduism and Sikhism, which still predominate the region making it a real mission land.

The Catholic community is itself a Kaleidoscopic picture of the variety of ethnic and cultural groups with independent linguistic identity, from different socio-economic background, yet united together in their faith in Christ around one pastor. Today the Diocese has 58 parishes and mission stations and the pastoral activities of these centers are taken care by altogether 140 priests of the Diocesan Clergy and priests of seven different Religious Congregations. The pastoral, educational and social activities are shared by 30 other congregations of Religious Brothers and Sisters spread in 61 communities.

With the appointment of Bishops Late Rt. Rev. Dr. Gilbert B. Rego and Rt.Rev. Dr. Gerald John Mathias, the Diocese of Simla-Chandigarh progressed well and now with the appointment of Most Rev. Ignatius Mascarenhas in 2009, the Diocese of Simla Chandigarh entered into a new phase of its history venturing into different missions and opening new institutions.