Born in the Travancore region of Kerala, Thomas was raised in the Mar Thoma Syrian Church, whose combination of ancient sacramental liturgy with modern evangelical spirituality undergirded his life and ministry. His early Christian youth work and social action in India projected him onto the scene after World War II. From 1947 to 1953 he was on the staff of the World Student Christian Federation in Geneva. The Christian in the World Struggle, written by Thomas in 1952 with colleague David McCaughey, was an influential guide to Christian student groups in its time.

Thomas served the World Council of Churches (WCC) as moderator of its Central Committee fro 1968 to 1975. Earlier, he was Asian staff member of the WCC church and society department, then chair of the departmental working committee and co-chair of the World Conference on Church and Society in Geneva, 1966. He was also secretary of the East Asia Christian Conference for church and society concerns. He was a tireless speaker and writer, stimulating ecumenical debate and forging consensus, expressed in countless conference and meeting reports he helped write. Towards a Theology of Contemporary Ecumenism (1978) presents some of this work.

In India, Thomas served as associate, then director, of the Christian Institute for the Study of Religion and Society from 1958 until his retirement in 1975. His work produced a library of studies and conference reports on the religious and social dimensions of Indian life in Christian perspective. He also wrote extensively in his own name, interpreting Christian faith in light of the Asian revolution, in Indian society, and in encounter with Hinduism and secular ideologies. In retirement, he continued to write biblical studies and theology in Malayalam, his mother tongue. He served as governor of Nagaland, by appointment of the government of India, from 1990 to 1992.

Charles C. West, “Thomas, M(adathilparampil) M(ammen),” in Biographical Dictionary of Christian Missions, ed. Gerald H. Anderson (New York: Macmillan Reference USA, 1998), 666-7.