Christianity in the state of Tamil Nadu, India is the second largest religion in the state. According to tradition, St. Thomas, one of the twelve apostles, landed in Malabar Coast (modern day Kerala) in AD 52. In the colonial age many Portuguese, Dutch, British and Italian Christians came to Tamil Nadu. Priests accompanied them not only to minister the colonisers but also to spread the Christian faith among the non-Christians in Tamil Nadu. Currently, Christians are a minority community comprising 6% of the total population. Christians are mainly concentrated in the southern districts of Tamil Nadu - Kanyakumari (47.7% of the population, 2011), Thoothukudi (19%, 2011) and Tirunelveli (15%, 2011).

The Catholic Church—including the Latin Church, Syro-Malabar Church, and Syro-Malankara Catholic Church—the Church of South India, the Pentecostals, The Salvation Army Church, the Jacobite Syrian Christian Church, the Malankara Orthodox Syrian Church, the Evangelical Church of India, the Apostolics, and other evangelical denominations constitute the Christian population in Tamil Nadu. The Latin Church of the Catholic Church has 18 dioceses including the Archdiocese of Madras and Mylapore and the Archdiocese of Madurai, and has a homogeneous presence throughout the state. The second-largest church by the number of members is the Church of South India with eight dioceses in Tamil Nadu. They are Coimbatore Diocese, Kanyakumari Diocese, Madras Diocese, Madurai-Ramnad Diocese, Thoothukudi – Nazareth Diocese, Tirunelveli Diocese, Trichy-Tanjore Diocese and the Vellore Diocese. Church of South India Synod, the highest administrative body of the Church of South India, is in Chennai. The vast majority of Christians in Tamil Nadu are either Latin Catholics or members of the Church of South India. The Pentecostal Mission (TPM) is headquartered in Chennai. The Congregational churches were a small group called The London Missionary Society (LMS) run under Travancore Church Council (TCC) with its headquarters in Nagercoil. The London Mission Congregational churches date back to 1795 when British missionaries were sent to 19th century Tamil Nadu and Kerala States of South India.

The Salvation Army is an International Christian Church and charitable organisation. There are six territories in India; Eastern, Western, Northern, Central, South Eastern and South Western Territory. Tamil Nadu and Pondicherry come under the Central and South Eastern Territory. There are more than 1000 churches over Tamil Nadu and Pondicherry. School, colleges, homes, shelters, and medical services are provided here. The Salvation Army does missionary, medical, educational, emergency disaster, and social services.

The Salvation Army operation commenced on 27 May 1892 as a result of the vision received by Major Deva Sundaram at "Medicine Hill" near Nagercoil in Kanyakumari District. He had been praying and fasting with three officers in South Tamil Nadu. As the Army experienced rapid growth in South India, the territory was separated from Southern Territory on 1 October 1970. States included in the territory: Tamil Nadu, Pondicherry. 'The Salvation Army' in Tamil: Ratchaniya Senai in Malayalam: Raksha Sainyam. Languages in which the gospel is preached: English, Malayalam, Tamil. Periodicals: Chiruveeran (Tamil), Home League Quarterly, Poresatham (Tamil), The Officer (Tamil)

In 1996, the Syro-Malabar Catholic Church created its first `Diocese of Thuckalay` in Kanyakumari district, (which was under the Syro-Malabar Catholic Archdiocese of Changanassery in Kerala till then), of Tamil Nadu. The same year the Syro-Malankara Catholic Church has also newly established the `Diocese of Marthandam` (bifurcated from its Archdiocese of Trivandrum) in Kanyakumari district. The Malankara Orthodox Syrian Church established its first diocese Chennai Diocese in the year 1979. St. Thomas Mount in Chennai, the place where St. Thomas, one of the disciples of Jesus Christ, was believed to have been martyred, is an important pilgrimage site for Indian Christians. The Santhome Basilica, supposedly built atop the tomb of St. Thomas, and the Vailankanni Basilica of Our Lady of Good Health—revered churches by India's Roman Catholics—are good examples of majestic church architectures in Tamil Nadu.

One of the disciples of Jesus Christ, St. Thomas introduced Christianity in Kanyakumari. He built a church in Thiruvithamcode in 63 AD. In the first half of the 16th century, thousands of fishermen converted to Catholicism due to the efforts of Francis Xavier. He built a church in Kottar, Nagercoil. In the 18th century (1806) European missionary William Tobias Ringeltaube established Protestant churches and propagated Christianity in Kanyakumari district and South Travancore. He built a first Protestant Church in mylaudy.

San Thome Basilica is a Roman Catholic (Latin Rite) minor basilica and one of the three National Shrines in India located in Santhome, Chennai city (Madras), India. It was built in the 1523 by Portuguese explorers, and rebuilt again with the status of a cathedral by the British in 1893. The British version still stands today. It was designed in Neo-Gothic style, favoured by British architects in the late 19th century. Christian tradition holds that St. Thomas arrived in Kerala & Kanyakumari Dist in 52 AD preached between 52 AD and 72 AD, when he was believed to be martyred on St. Thomas Mount. The basilica is built over the site where he was believed originally to be interred.

San Thome Basilica is the principal church of the Madras-Mylapore Catholic Archdiocese. In 1956, Pope Pius XII raised the church to the status of a Minor Basilica, and on 11 February 2006, it was declared a national shrine by the Catholic Bishops' Conference of India. The San Thome Basilica is a pilgrimage centre for Christians in India. This church is a very important site in the world for Christians. The church also has an attached museum at back.