He was mainly concerned with questions of ecumenism, however also serving as president of the Vatican Secretariat for Non-Believers (which in 1993 was united with the Pontifical Council for Culture) from 6 April 1965 until his resignation on 27 June 1980.

A year and a half later, in 1980, he received a position in the Roman Curia, the Holy See's governing body, as Pro-President of the Secretariat for Non-Believers, later (in 1988) renamed the Pontifical Council for Culture.