St. Thomas' Cathedral is the seat of the Jaffna Diocese of the Church of South India located in Vaddukoddai, Sri Lanka.

Portuguese Jesuits built a Catholic church in Vaddukoddai in the 1660s which was later taken over and renovated by the Dutch before being handed over to the American Ceylon Mission (ACM) by the British.

[1][2] In May 1904 the Congregational Council of Ceylon (CCC) was set-up to administer ACM's churches.

[3][4] CCC joined together with the American Madura Mission and the London Missionary Society in Travancore to form the United Churches of South India and Ceylon (UCSIC) in 1905.

[3][4][5][6] The cathedral was declared an archaeological protected monument in December 2011.