He was created Cardinal-Priest of Santa Balbina by John Paul II in the consistory of 21 October 2003. He was the youngest cardinal member of the Sacred College until the appointment of Reinhard Marx in 2010. Erdő was one of the cardinal electors who participated in the 2013 papal conclave that selected Pope Francis, and can continue to exercise his right to vote in any future conclave until his 80th birthday on 25 June 2032. Erdő was elected President of the Hungarian Episcopal Conference in September 2005 for a five-year term, and President of the Council of Episcopal Conferences of Europe in October 2006 for the same period of time. On 17 January 2009 he was appointed a member of the Pontifical Council for Culture by Pope Benedict, and on 29 January 2011 of the Secretariat of State. Erdő sponsored the Thirteenth International Congress of Medieval Canon Law, in Esztergom, 3–9 August 2008. On 19 October 2011, the apostolic nunciature in Peru announced that he was going to be apostolic visitor to intervene in the dispute between the Pontifical Catholic University of Peru and the Archdiocese of Lima. This was a controversial choice since the Archbishop of LimaJuan Luis Cipriani Thorne is a member of the same Opus Dei personal prelature that, through the Opus Dei's University of Navarra, granted Erdő a doctor honoris causa degree in that same year. On Tuesday, 18 September 2012, Erdő was appointed by Pope Benedict XVI to be one of the Synod Fathers for the upcoming October 2012 Ordinary General Assembly of the Synod of Bishops on the New Evangelization. Erdő had been mentioned as a possible candidate to be elected pope during the papal conclave 2013. On Monday 14 October 2013, Erdő was named by Pope Francis to serve as the Relator General of the Third Extraordinary General Assembly of the Synod of Bishops, which took place from 5 to 19 October 2014. The chosen theme is "The challenges of the family in the context of evangelization". He resumed his appointment as Relator General when the Synod reconvened in October 2015. In the 2015 book The Rigging Of A Synod?, Vatican correspondent Edward Pentin claimed that Cardinal Lorenzo Baldisseri had pressured Erdő to soften the wording of his 2014 address to the Synod. In 2015, Erdő's second address to the synod was described by journalists, such as Damian Thompson of The Spectator and John L. Allen, Jr. of the Boston Globe, as more theologically conservative in its tone.
Views
Cardinal Mindszenty
Erdő requested that the Hungarian Chief Prosecutor's Office legally, morally and politically rehabilitate Cardinal Jozsef Mindszenty, his predecessor, who fought Hungary's communist regime and was arrested by the country's Stalinist dictatorship, after which he sought refuge in the American embassy in Budapest. The Chief Prosecutor's Office ultimately rehabilitated Mindszenty in 2012 thanks to Erdő's intervention. In 2006, he sent a letter of gratitude to president George W. Bush on the 50th anniversary of Cardinal Mindszenty's forced arrest because of the political support that Americans had granted to Mindszenty at the time.
Divorced and remarried Catholics
During a Vatican press conference in October 2014, Erdő expressed opposition to the idea of allowing divorced and remarried Catholics to receive Holy Communion. Erdő, who is the Relator General at the Third Extraordinary General Assembly of the Synod of Bishops told journalists at a press conference in Rome that the Catholic Church will not change its policy on the matter after the synod.
Erdő has written about the special socio-economic conditions of the Romani people and has openly wondered on the correct way to evangelize them.
Church in Hungary
Erdő has focused on Hungary's need to restore its faith and hope, while celebrating Midnight Mass at St. Stephen's Basilica in Budapest, to mark the Christmas holiday.