The roots of Christianity in the diocese appear to go back to the times of St. Thomas and St. Francis Xavier. Tradition at Devipattinam on the sea coast near Ramnad is that St. Francis Xavier alighted and celebrated Mass here in 1545 on his way from Mannar in Sri Lanka to Santhome, in Chennai, India, and that he also started the conversion of the Kadayars on what is now Rameswaram Island in Ramanathapuram district, part of Sivagangai diocese.
In the last decade of the 16th century, the Xaverian Mission on the pearl fishery coast set up a residence at Periapatnam and a small mission at Thirupalakudion in Ramnad. It was during this period that St. John de Britto, the patron saint of the diocese, toiled, preaching and converting multitudes at the cost of privations, hardships and persecutions. He was later tortured and beheaded in Oriyur after a painful imprisonment.
However, confusion prevailed in the area after the Society of Jesus was banned. The tussle between Padroado (a mission agency of Portuguese with patronage rights granted to it by the Holy See) and Propaganda (a mission agency encouraged by the Holy See based at Pondicherry) created more confusion in this area.
However, in 1929, all types of "double" jurisdictions were suppressed and peace prevailed in the Madurai Mission. After the formation of the Indian Hierarchy in 1887, Monsignor Alexis Canoz became the Titular Bishop of Trichy. In 1923, Tuticorin diocese was erected. In 1938, Monsignor Peter Leonard worked out and effected the carving out of the then Diocese of Madurai from Trichy and became its first bishop. In 1973, the Diocese of Palayamkottai was carved out as a separate diocese from Madurai. And finally on July 25, 1987, Pope John Paul II decreed the erection of the Diocese of Sivagangai which was carved out of the Archdiocese of Madurai. Father Edward Francis was elected the first bishop of Sivagangai. He served the diocese for 18 years. Father Susaimanickam was appointed coadjutor bishop in May 2005 and became bishop in September 2005.
The population in Sivagangai was 2,727,000 as of the end of 2017. (The population of the whole country is about 20 million). Most residents are ethnic Tamils. Recently there has been an increase in the number of refugees from war-torn Sri Lanka.
The towns are managed by municipalities. The villages and small towns are administered by elected local bodies called panchayats.
The diocesan area is well connected in terms of roads and railways. The nearest airport is in Madurai.
The diocesan territory covers 8,353 square kilometers and includes the civil districts of Sivagangai and Ramanathapuram. Sivagangai, Karaikudi and Rameswaram are considered major towns. This area falls under the rain shadow region of Tamil Nadu and receives less rainfall than other areas.
The per capita income in the diocese territory was 15,699 rupees (US$342 as of September 2006). Farming and fishing are the major occupations here. Horticulture is also given much importance. Tourism is a vital money earner for the area. Rameswaram is an important Hindu pilgrimage center here and it attracts a large number of pilgrims from all over India and the rest of the world.
Government and private operators provide extensive telecommunication facilities in the diocesan area. The diocese is well connected by local cable TV networks.
The literacy rate is 72.57 percent.