The historian Kenneth Setton called him "one of the commanding figures of his day, and the letters of Petrarch abound with references to him".

[6] On 11 October 1340, Pope Benedict XII approved Guy's election as Archbishop of Lyon,[7] and he was duly consecrated,[8] but he held the Archbishopric for less than two years, surrendering it when he became a cardinal and moved to Avignon.

[9] In the Consistory of 20 September 1342, Pope Clement VI (Pierre Roger) named ten new cardinals, among them Archbishop Guy de Boulogne.

On 6 and 7 November, he was present in Consistory when the financial obligations of the newly appointed Archbishop of Narbonne, the Papal Chamberlain Gasperto du Val, were settled by the Pope.

The two kingdoms had been at war since the murder of the Hungarian prince Andrea, Duke of Calabria, husband of the Angevin Queen of Naples, Joanna I, in 1345.

Naples had been conquered by Andrew's elder brother Louis I of Hungary, and Joanna was forced to flee to Provence, her ancestral home.

[28] On 25 May, Pope Clement wrote a letter to King Louis of Hungary, in the belief that Cardinal Guy was still in Italy; he had not yet returned to Avignon.

[30] King Louis of Hungary, on his way home from his failed Neapolitan campaign, visited Rome for the Jubilee, and was back in Buda on 25 October 1350.

[32] In 1351, from his prison in Prague, where he had gone to seek support from the Emperor Charles IV, Cola di Rienzi wrote a letter to Guy requesting his assistance in obtaining his freedom and leading a crusade.

[34] On 15 May 1352, Cardinal Guy was present at the Curia in Avignon, where he presided over the blessing of the new Abbot of l'Isle-Barbe near Lyon, Jean Pilfort de Rabastencs.

The Conclave to elect his successor opened on Sunday, 16 December 1352 in the Apostolic Palace in Avignon, with twenty-six cardinals in attendance, including Guy de Boulogne.

[37] Immediately after his coronation on 30 December 1352, the new Pope, Innocent VI, appointed Cardinal Guy as the principal facilitator in negotiations between the English and the French for an end to the war.

[38] Cardinal Guy was attempting to use all of his credit with the French monarchy to bring about a peace with England, which would greatly enhance his prestige.

[40] On 6 April 1354 at Guînes, Cardinal Guy de Boulogne witnessed the signing by representatives of France and England of a preliminary accord for ending the Hundred Years' War.

Pope Innocent VI had made numerous demands for his release, and this was one of the purposes of Cardinal Guy's legation.

[44] In the end a compromise candidate was elected, Abbot Guillaume Grimoald of S. Vincent in Marseille, who was Legate of the Apostolic See in the Kingdom of Sicily, and was not present at the Conclave.

The party stopped in Viterbo while Pope Urban took the body of his late friend Cardinal Egidio Albornoz, who had died on 24 August, to Assisi, where he had wished to be buried in the Basilica of S. Francesco.

The Emperor Charles IV paid a visit during this time,[49] and, on All Saints Day, 1 November 1368, the Pope crowned the Empress Elizabeth in the Vatican Basilica.

[54] On 13 June 1369, Cardinal Guy was named Emperor Charles' Vicar General of Lucca and its territory for a period of three years.

[55] In Lucca Guy established his headquarters while he served as "Lieutenant and General Vicar" for the Empire "in the regions [lit.

[56] On 21 December 1370, Guy gave a eulogy, prepared in a single day, at the funeral of Urban V in the church of Notre-Dame-des-Doms in Avignon.

[57] On 30 December, Cardinal Pierre Roger de Beaufort, a nephew of Clement VI, was elected to succeed Urban.

('Today they named me by the method of the Holy Spirit')[58] On 4 January 1371, Cardinal Guy de Boulogne, Bishop of Porto and Santa Rufina, ordained him a priest.

[61] His body was returned to France by his brother, Jean Comte d'Auvergne et du Boulogne, and he was buried at the Abbey of Notre-Dame de Bouchet in the diocese of Clermont.

Cardinal Guy de Boulogne had left the abbey sufficient money to finish his tomb, as well as a legacy to purchase enough property to support twelve monks.