Pope Francis has beatified one of his predecessors, John Paul I – a briefly serving pontiff who distinguished himself with his humility and cheerfulness, and whose abrupt death in his bedroom in 1978 shocked the world and fuelled suspicions for years about his demise.

The ceremony in St Peter’s Square on Sunday constituted the last formal step in the Vatican before possible sainthood for Albino Luciani, an Italian who died 33 days after being elected pontiff.

John Paul I “with a smile, communicated the goodness of the Lord”, Francis said in his homily.

Francis encouraged people to pray to the newly beatified churchman to “obtain for us the smile of the soul”.

Last year, Francis approved a miracle attributed to the intercession of John Paul I – that of the recovery of a critically ill 11-year-old girl in 2011 in Buenos Aires.

Now a young woman, Candela Giarda told a Vatican press conference last week in a video message that she had wanted to attend the ceremony but could not because she recently broke her foot while training in a gym.

Seated under a canopy outside St Peter’s Basilica, Francis led the ceremony, which was punctuated by booms of thunder, flashes of lightning and pouring rain, prompting cardinals, bishops, the choir and thousands of rank-and-file faithful in the square to open umbrellas.

When elected pontiff on August 26, 1978, Luciani, 65, had been serving as patriarch of Venice, one of the church’s more prestigious positions.

In that role as well as that previously as a bishop in north-eastern Italy, Luciani sounded warnings against corruption, including in banking circles.

In his short-lived papacy, which concluded with the discovery of his body in his bedroom in the Apostolic Palace, John Paul I immediately established a simple, direct way of communicating with the faithful in the addresses he gave, a style change considered revolutionary considering the stuffiness of church hierarchy.

Those who have campaigned for him to be made a saint have stressed his deep spirituality and his tireless emphasis on key Christian virtues – faith, hope and charity.

“Let us pray, in his own words: ‘Lord take me as I am, with my defects, with my shortcomings, but make me become what you want me to be,'” Francis said.

John Paul “lived without compromise”, Francis said, hailing Luciani for having ”conquered the temptation to put one’s ‘I’ at the centre or to seek glory”.

Although the Vatican said John Paul died of a heart attack, it gave conflicting versions of the circumstances of how his body was discovered.

First it said a priest who served as his secretary found him, but it later acknowledged John Paul was found dead by one of the nuns who brought him his customary morning coffee.

With a huge financial scandal developing at the time in Italy involving figures who had links to the Vatican’s bank, suspicions quickly took root in the secular media that perhaps Luciani was poisoned because he intended to root-out wrongdoing.

Books speculating on the circumstances surrounding his death, especially since no post-mortem was carried out, sold millions of copies.