Pope Paul VI created him Cardinal Priest of "Santi Nereo e Achilleo" in the consistory of February 22, 1965. Cooray, the first Sri Lankan member of the College of Cardinals, resigned as Colombo's archbishop on September 2, 1976, after a period of twenty-nine years. He was one of the cardinal electors who participated in the conclaves of August and October 1978, which selected Popes John Paul I and John Paul II respectively, and the first Sri Lankan to participate in the election of a Pope.