The Second Council of Lyon was the fourteenth ecumenical council of the Roman Catholic Church, convoked on 31 March 1272 and convened in Lyon, Kingdom of Arles, in 1274. Pope Gregory X presided over the council, called to act on a pledge by Byzantine emperor Michael VIII to reunite the Eastern church with the West. The council was attended by about 300 bishops, 60 abbots and more than a thousand prelates or their procurators, among whom were the representatives of the universities. Due to the great number of attendees, those who had come to Lyon without being specifically summoned were given "leave to depart with the blessing of God" and of the Pope. Among others who attended the council were James I of Aragon, the ambassador of the Emperor Michael VIII Palaiologos with members of the Greek clergy and the ambassadors of Abaqa Khan of the Ilkhanate. Thomas Aquinas had been summoned to the council, but died en route at Fossanova Abbey. Bonaventure was present at the first four sessions but died at Lyon on 15 July 1274. As at the First Council of Lyon, Thomas Cantilupe was an English attendee and a papal chaplain.

Pope Gregory X, born Teobaldo Visconti, was head of the Catholic Church and ruler of the Papal States from 1 September 1271 to his death and was a member of the Secular Franciscan Order. He was elected at the conclusion of a papal election that ran from 1268 to 1271, the longest papal election in the history of the Catholic Church.