The Papal conclave of 1846 elects Pope Pius IX, beginning the longest reign in the history of the papacy.

The 1846 papal conclave was triggered after death of Pope Gregory XVI on 1 June 1846. Fifty of the 62 members of the College of Cardinals assembled in the Quirinal Palace, one of the papal palaces in Rome and the seat of two earlier 19th century conclaves. The conclave began on 14 June and had to elect a pope who would not only be head of the Catholic Church but also the head of state and government of the Papal States, the extensive lands around Rome and Northern Italy which the Catholic Church governed.