Pope Paul VI appointed him to the
Roman Curia and gave him a series of assignments, starting as adjunct secretary of the
Congregation for the Evangelization of Peoples in 1971 and secretary of that Congregation in 1973. On 19 December 1975 he was named Vice President of the
Pontifical Council for Justice and Peace and on 5 January 1976 Gantin received the additional responsibilities of the Vice President of the Pontifical Council
Cor Unum, as Pope Paul was combining those two departments. On 4 September 1978, he was named President of the Pontifical Council
Cor Unum by
Pope John Paul I, the only administrative appointment of his month-long papacy. Gantin met with John Paul I the day before he died. At the first of them he was reportedly one of three cardinals who counted the votes. During the second of these conclaves, Gantin was thought to be one of the
papabili, those cardinals who are thought to have a chance of being elected pope. (Lodi),
Italy, 1984 In 1982, he accompanied Pope John Paul II on his visit to Benin. which supervises episcopal appointments in the non-missionary
Latin Rite dioceses throughout the world. He was also made president of the
Pontifical Commission for Latin America. On 25 June 1984, Gantin opted to become a member of the order of cardinal priests. For the next fourteen years he collaborated with Pope John Paul in shaping the hierarchy of the Church, both in making appointments and in managing the agendas for the periodic visits bishops make to consult with the pope and the Curia. On the pope's behalf he managed appointments of conservative prelates in dioceses that did not welcome them in the Netherlands and Switzerland, removed an outspoken liberal French bishop, contended with Latin American advocates for the rights of indigenous peoples, and the excommunication of
Marcel Lefebvre, with whom he had worked in Africa in the 1960s. ==Cardinal bishop and dean==