Cardinal electors in the 1978 conclaves

The papal conclaves of August 1978 and of October 1978 were convened to elect a pope, the leader of the Catholic Church, to succeed Paul VI and John Paul I following their respective deaths on 6 August 1978 and on 28 September 1978. In accordance with the apostolic constitution Romano Pontifici eligendo, which governed the vacancy of the Holy See, only cardinals who had not passed their 80th birthday on the day on which the conclave began (in these cases, those who were born on or after 25 August 1898 for the first conclave, and on or after 14 October 1898 for the second conclave) were eligible to participate. Although not formal requirements, the cardinal electors invariably elect the pope from among their number. The election was carried out by secret ballot (Latin: per scrutinium). Due to the brief duration between the conclaves, the respective lists of cardinal electors are nearly identical.

Of the 129 members of the College of Cardinals at the time of the beginning of the first conclave, 114 cardinal electors were eligible to participate in the subsequent conclave. Three cardinal electors did not attend, decreasing the number of participants to 111. Two cardinal electors died in the time between the conclaves. Of the 126 members of the College of Cardinals at the time of the beginning of the second conclave, 111 cardinal electors were eligible to participate in the subsequent conclave; all of whom were in attendance. The required two-thirds-plus-one supermajority needed to elect a pope in either conclave was 75 votes.

Of the 112 cardinal electors who attended at least one of the two conclaves, 5 were cardinal bishops, 92 were cardinal priests, and 15 were cardinal deacons; 3 had been created cardinals by Pope Pius XII, 8 by Pope John XXIII, and 101 by Pope Paul VI; 28 worked in the service of the Holy See (such as in the Roman Curia), 77 were in pastoral ministry outside Rome, and 10 had retired. The oldest cardinal elector in the conclaves was Joseph-Marie Trịnh Như Khuê, at the age of 79, and the youngest was Jaime Lachica Sin, at the age of 49–50. Another 15 cardinals were ineligible to participate in either conclave for reasons of age.

The cardinal electors entered the Sistine Chapel to begin the first conclave on 25 August 1978. On 26 August, after four ballots over two days, they elected Cardinal Albino Luciani, the patriarch of Venice, who took the papal name John Paul I. After his death 33 days into his papacy, the cardinal electors again entered the Sistine Chapel to begin the second conclave on 14 October. On 16 October, after eight ballots over three days, they elected Cardinal Karol Wojtyła, the archbishop of Kraków, who took the papal name John Paul II.