The church of St. Thomas Christians is an Apostolic Church founded in India by St. Thomas, one of the twelve apostles of Christ. According to ancient, strong and cotinuous traditions, St. Thomas landed at Kodungalloor (Muziris) in 52 A.D. After preaching and establishing Christian communities in different parts of India, he suffered martyrdom at Mylapur in 72 A.D. Tradition holds that St. Thomas founded seven churches in Kerala; at Kodungalloor, Niranam, Kollam, Chayal, Kottakkavu, Kokkamangalam and Palayoor. Even before the Christian era, there were Jewish colonies in South India and we see with amazement the strange coincidence that these seven churches are situated in or near these colonies. From early centuries the Church of St. Thomas Christians came into life-relation with the Christian communities that came to be known as East Syrian Church.

This relationship made the St. Thomas Christians share the liturgical, spiritual and other ecclesiastical traditions with the East Syrian Church (therefore they are grouped under Chaldean Rite). At the same time the Christians of St. Thomas kept their distinctive character especially in Church administration and socio-cultural and ascetic- spiritual life.
Knanaya Catholics of Syro-Malabar Church claim their origin to Thomas of Cana and the 72 families that migrated to Kerala in 345 A.D. from the land of Syria. The descendants of this group maintained their separate identity. In the matter of liturgy and spiritual activities they fully belong to the Syro-Malabar Church and as such they are an integral part of it. His Holiness Pope Pius X established the diocese of Kottayam in Kerala for this endogamous group in 1911.

Though today the Syro-Malabarians are found mainly in the southern state of Kerala and in the big cities of India there are evidences to believe that there were communities of these Christian in other parts of India right from early centuries. For some reasons unknown to us, they ceased to exist. These Christians were well established and integrated in the fabric of the society at large. In the early centuries their main occupations are believed to have been military services to the local kings, trade or agriculture. However, this is no more so today.