 Sitting on the Conciliar preparatory commissions for seminaries and universities, Colombo attended the Second Vatican Council (1962–1965), during the course of which he was named by Pope Paul VI to succeed him as Archbishop of Milan on 10 August 1963.Along with Bernardus Johannes Alfrink, he assisted Achille Liénart in delivering one of the closing messages of the Council on 8 December 1965.He was created Cardinal-Priest of "Ss.