Dubbed "the smiling pope", John Paul I served as pontiff from 26th August 1978 to his sudden death 33 days later, which quickly became fertile ground for conspiracy theorists.
Acknowledging his official virtues is a step before beatification, which is reserved for three categories of people: martyrs, those who have lived a life of heroic values, and others with a clear saintly reputation.
Candidates must also be credited with a miracle after their death. Those beatified can then move towards sainthood.
Francis signed a decree on Wednesday declaring John Paul I "venerable". He now needs the Roman Catholic Church to recognise a first miracle in his name.
Born Albino Luciani, the son of a bricklayer, he was the last Italian pope and a particularly warm and pastoral figure.
He is perhaps best known, however, for his death, which quickly attracted a series of rumours ranging from his murder by dark forces linked to a corrupt Vatican bank, to suicide by a man who did not want to be pope.
Stefania Falasca, a journalist for Avvenire, the Italian Catholic daily newspaper, said on Wednesday that the conspiracy was fuelled by a lack of transparency on the Vatican's part in the hours immediately following the
She says his body was found early morning by the sister who brought him his coffee, but the Vatican balked at the idea of telling the world a woman had been in his bedroom and seen the body, so they changed the story.
The inconsistencies that later emerged in the time-line drove some to believe the Church was hiding a dark secret.