Also known as Moran Mor Baselios Cardinal Cleemis Catholicos, the 53-year-old Thottunkal is the archbishop of Thiruvananthapuram, capital of Kerala state in southern India. He was one of the last cardinals appointed by Benedict in November 2012.
Thottunkal is the first cardinal of the Syro-Malankar rite, a West Syrian Rite Eastern Catholic Church in full communion with the Holy See, which has a total membership of around 500,000.
Benedict, who abdicated at the end of February, also appointed Thottunkal a member of the Congregation for the Oriental Churches and the Pontifical Council for Interreligious Dialogue.
Cardinal Walter Kasper, who turned 80 after Benedict abdicated, is the conclave's oldest cardinal elector. The electors' average age is 72.
Since 1975, cardinals over 80 have been excluded from voting in papal conclaves.
Italy's cardinal Angelo Scola, the archbishop of Milan, enters as the favourite to be elected pope.