The papal conclave held from 24 February to 31 March 1829 to elect a successor to the recently deceased Leo XII resulted in the accession of Cardinal Francesco Castiglioni, who took the name Pius VIII.

Cardinal Emmanuele De Gregorio was the proposed candidate of the pro-French faction and the zelanti (conservative cardinals), whilst Cardinal Bartolomeo Pacca was proposed by the more moderate cardinals but was not accepted by the French government of the Bourbon Restoration period, headed by King Charles X and Prime Minister Jean Baptiste Gay, vicomte de Martignac.

The arrival of Giuseppe Albani caused the votes to center on Francesco Saverio Castiglioni.

Castiglioni had been close to election in the 1823 conclave as the representative of the politicanti (moderate cardinals) and had all the qualifications to become Pope, though he had the problem of being in very poor health, but was not elected at the last conclave when the zelanti Cardinals came to realize that he was quite close to Cardinal Ercole Consalvi.

[1][2] Consalvi however was already dead by the time of the 1829 conclave having died during the pontificate of Pope Leo XII.