From 1947 until his death he held various offices in the Roman Curia, including Secretary General of the Second Vatican Council, head of the Pontifical Commission for the Revision of the Code of Canon Law, and from 1977 Prefect of the Supreme Tribunal of the Apostolic Signatura.

He earned degrees in philosophy, theology and canon law and then served for ten years as rector of the Pontifical Roman Seminary.

He described its work as current issues rather than questions of church practice and said journalists would be welcome to report freely: "The Pope wants all opinions, even if contrary to the doctrine, experience and jurisprudence of the Roman curia.

"[5] Cardinal Roberto Tucci recorded in his diaries that Pope John described Felici as very learned and a hard worker, adding that "he has a narrow mind".

[9] He made announcements to the assembled bishops about their agenda and procedures in Latin,[10] as well as the results of balloting when voting began in late 1963.

[11] In 1962, during its first session, he prevented the distribution of copies of a speech scheduled for delivery by Helder Pessoa Camara, then Auxiliary Bishop of Roman Catholic Archdiocese of Rio de Janeiro, because it criticized the council's failure to address social issues.

[17] He was also a member of the Vatican commission that reviewed the new catechism produced by the Dutch bishops in 1967 and sought clarifications before allowing it to be translated into other languages.

[18] Beginning on 21 February 1967, he headed the Pontifical Commission for the Revision of the Code of Canon Law,[a][20][21] a task completed a few months before his death.

It was, wrote one journalist, "vigorously and even bitterly criticized by canon lawyers and others" who described it as "overly authoritarian" and complained that it "committed the church to single outdated view of itself at a time when the subject is still a source of considerable disagreement among theologians".

"[24][b] Felici appeared in a more collaborative context in 1970 when he joined Cardinal Johannes Willebrands in announcing somewhat relaxed rules for Catholics who marry non-Catholics.

[2] On 26 June 1967, Pope Paul VI elevated him to the rank of cardinal and made Cardinal-Deacon of Sant'Apollinare alle Terme Neroniane-Alessandrine.

"[37] In a speech approved by Pope John Paul II, he reported to the Synod that marriage annulments were rapidly increasing and that lower courts were failing to uphold standards and using excuses like "psychological immaturity".