The decision to found the monastery dates back to the 12th of December, 1609, although Laconi had been listed as host town. The person of Father Pietro Locci was important for the preference of Genoni to Laconi: he also convinced the Marquis of Laconi in that decision, while the approval by the competent Ecclesiastical Authority was given on 20th of July, 1638.
The official mandate to Father Pietro Locci to found the new St. Sebastian monastery in Genoni dates back to the 28th of October, 1638. The memorandum is dated 14th of October, 1638.
The two ancient churches of St. Sebastian Martyr and the Sacred Sepulchre (so named because next to the cemetery) were the area chosen to build the monastery; the churches were united. A third church was built, in honour of St. Sebastian Martyr, which gave the name and title to the monastery. The inhabitants of Genoni aided in its construction for free, with a working day each, as determined by the chapters of understanding between the Friars Minor of Sardinia and the People and the Community of Genoni. The conditions of the Friars to the Community were:
- a stable and permanent presence of a Franciscan community, made up of no less than 12 friars, whose main task would be pastoral work
- a stable Preacher throughout the year for preaching Lent, Advent and every other Christian feast of the Parish
- a Grammar teacher for Genoni pupils and in the future to open a study of Rhetoric and Philosophy
- the collaboration and involvement with the community in all pastoral and spiritual commitment of the town
At the beginning the relationship between the religious men and the land was fruitful; the monastery also owned land, so that the Friars could apply the fruits resulting from masses. Its cultural role within the Community was also important. In 1778 a list of volumes in the monastery Library was compiled, giving a total of 413 volumes divided into sections: Sacred Scripture, Moral Theology, Mystical Theology, Philosophy, History, Hagiography, Preaching, Liturgy, Franciscan, Mariology, Theology sacramental, Classic Literature, Grammar and Rhetoric.
From the late eighteenth early nineteenth century, however, the monastery of St. Sebastian went into decay. Around 1840 Casalis notes that "the brothers are now reduced to three or four from the many they were before." This was due to misunderstandings born between the religious men and the Municipality of Genoni, based on mutual accusations of negligence and breach of covenants and initial conditions. The brothers were accused of not fulfilling education roles with young people as they did before, while the administration was reprimanded for not remunerating the monastery teachers.
In 1862 the monasteries of the Province of San Saturnino (of which Genoni was part) were suppressed by the Italian Government.