コンスタンツ公会議
After deposing Antipope John XXIII in 1415, the Council of Constance was long divided by the conflicting claims of Pope Gregory XII (1406–15) and Antipope Benedict XIII (1394–1423). Martin was elected pope, at the age of 48, at the Council of Constance on St. Martin's Day, 11 November 1417. Participants in the conclave included 23 cardinals and 30 delegates of the council. He was ordained a priest on 13 November, 1417, and consecrated bishop the next day.