In Italy he is remembered with the appellatives of "Il Papa del Sorriso" (The Smiling Pope) and "Il Sorriso di Dio" (God's Smile). Time magazine and other publications referred to him as The September Pope.

Albino Luciani was born on 17 October 1912 in Forno di Canale (now Canale d'Agordo) in Belluno, a province of the Veneto region in northern Italy. He was the son of Giovanni Luciani (1872? - 1952), a bricklayer, and Bortola Tancon (1879? - 1948). Albino was followed by two brothers, Federico (1915–1916) and Edoardo (1917–2008), and a sister, Antonia (b. 1920).

Luciani entered the minor seminary of Feltre in 1923, where his teachers found him "too lively", and later went on to the major seminary of Belluno. During his stay at Belluno, he attempted to join the Jesuits but was denied by the seminary's rector, Bishop Giosuè Cattarossi. Ordained a priest on 7 July 1935, Luciani then served as a curate in his native Forno de Canale before becoming a professor and the vice-rector of the Belluno seminary in 1937. Among the different subjects, he taught dogmatic and moral theology, canon law, and sacred art.

In 1941, Luciani began to seek a doctorate in theology from the Pontifical Gregorian University, which required at least one year's attendance in Rome. However, the seminary's superiors wanted him to continue teaching during his doctoral studies; the situation was resolved by a special dispensation of Pope Pius XII himself, on 27 March 1941. His thesis (The origin of the human soul according to Antonio Rosmini) largely attacked Rosmini's theology, and earned him his doctorate magna cum laude.

In 1947, he was named vicar general to Bishop Girolamo Bortignon, OFM Cap, of Belluno. Two years later, in 1949, he was placed in charge of diocesan catechetics.

On 15 December 1958, Luciani was appointed Bishop of Vittorio Veneto by Pope John XXIII. He received his episcopal consecration on the following 27 December from Pope John himself, with Bishops Bortignon and Gioacchino Muccin serving as co-consecrators. As a bishop, he participated in all the sessions of the Second Vatican Council (1962–1965).

On 15 December 1969, he was appointed Patriarch of Venice by Pope Paul VI and took possession of the archdiocese on 3 February 1970. Pope Paul created Luciani Cardinal-Priest of S. Marco in the consistory of 5 March 1973. Catholics were struck by his humility, a prime example being his embarrassment when Paul VI once removed his papal stole and put it on Patriarch Luciani. He recalls the occasion in his first Angelus thus:

Luciani was elected on the fourth ballot of the August 1978 papal conclave. Senior Cardinal Deacon Pericle Felici announced that the Cardinals had elected Venice patriarch Albino Luciani to be Pope John Paul I. After considering calling himself Pius XIII, he chose the regnal name of John Paul, the first double name in the history of the papacy, explaining in his Angelus that he took it as a thankful honour to his two immediate predecessors: John XXIII, who had named him a bishop, and Paul VI, who had named him Patriarch of Venice and a cardinal. He was also the first (and so far only) pope to use "the first" in his regnal name.

Observers have suggested that his selection was linked to the rumored divisions between rival camps within the College of Cardinals:

Outside the Italians, who were experiencing diminished influence within the increasingly internationalist College of Cardinals, were figures like Cardinal Karol Wojtyła. Over the days following the conclave, cardinals effectively declared that with general great joy they had elected "God's candidate". Argentine Cardinal Eduardo Francisco Pironio stated that, "We were witnesses of a moral miracle." And later, Mother Teresa commented: "He has been the greatest gift of God, a sunray of God's love shining in the darkness of the world."