Karol Wojtyła was ordained a priest on November 1, 1946. He taught ethics at the Jagiellonian University in Kraków and subsequently at the Catholic University of Lublin. In 1958 he was named auxiliary Bishop of Kraków and four years later he assumed leadership of the diocese with the title of Vicar Capitular. On December 30, 1963, Pope Paul VI appointed him Archbishop of Kraków. As both bishop and archbishop, Wojtyła participated in the Second Vatican Council, making contributions to the documents that would become the Decree on Religious Freedom (Dignitatis Humanae) and the Pastoral Constitution on the Church in the Modern World (Gaudium et Spes), two of the most historic and influential products of the council.

In 1967 Pope Paul VI elevated him to cardinal. In August 1978, following Paul's death, he participated in the Papal Conclave that elected Albino Luciani, the Cardinal Patriarch of Venice, as Pope John Paul I. At 65, Luciani was a young man by Papal standards. While Wojtyła at 58 could have expected to participate in another Papal conclave before reaching the age of eighty (the upper age limit for cardinal electors), he could hardly have expected that his second conclave would come so soon, for on 28 September 1978, after only 33 days in the papacy, Pope John Paul I died. In October 1978 Wojtyła returned to Vatican City to participate in the second conclave in less than two months.

The second conclave was divided between two particularly strong candidates for the papacy: Giuseppe Cardinal Siri, the Archbishop of Genoa, and Giovanni Cardinal Benelli, the Archbishop of Florence and a close associate of Pope John Paul I. In early ballots, Benelli came within nine votes of victory. However Wojtyła secured election as a compromise candidate, in part through the support of Franz Cardinal König amongst others who had previously supported Giuseppe Cardinal Siri. See Papal conclave, 1978 (October)