Centred at Chennai, the site associated with the martyrdom of St. Thomas, the Diocese of Madras has repeatedly been reorganised and now serves Tamil Nadu, the Andaman and Nicobar Islands, and parts of the Emirates.
The Diocese of Madras originated in the outside-Kerala division (Bahya Kerala Bhadrasanam) of 1938, and a separate Diocese of Madras was formed in 1979, with H.G. Zachariah Mar Dionysius as Metropolitan. Centred at Chennai, a region hallowed by the martyrdom of St. Thomas the Apostle, it originally embraced a vast territory that expanded with migration to include Tamil Nadu, the Andaman and Nicobar Islands, and overseas Australia, New Zealand, Malaysia, Singapore and Sri Lanka. Its growth required successive adjustments, including the formation of the Bangalore and Brahmavar dioceses in 2009–2010.
The Diocese of Asia–Pacific, established on 1 November 2024 by directive of Catholicos Baselios Marthoma Mathews III, took over Australia, New Zealand, Malaysia and Singapore, and in 2026 the missions in Sri Lanka were also transferred to it. In 2026 the churches in the Emirates of Sharjah, Ajman and Umm Al Quwain were placed under the Diocese of Madras.
4 districts, listed alphabetically.