John was born in Voltaggio, diocese of Genoa, Italy, in 1698. He was one of four children of Carlo de Rossi and Francesca Anfosi, who were poor, but pious parents. At the age of ten, he was taken in by wealthy friends of the family who saw to it that he was well-educated.
At the suggestion of his uncle, Lorenzo de Rossi, a Church Canon, John travelled to Rome to study at the Collegium Romanum, under the Jesuits. He entered the Roman College at 13 and completed the classical course of studies but began practicing severe mortification. This practice, combined with a heavy course load and a bout of epilepsy, led to a breakdown, and he was forced to leave the college. He recuperated and completed his training at Minerva but never fully regained his former strength.
At the age of 23 he was ordained (with dispensation, due to his poor health),and celebrated his first Mass in the Roman College. He was assigned to Rome, where he worked with the poor and the sick. He concentrated especially on the hospice of Saint Galla, an overnight shelter for paupers that had been founded by Pope Celestine III. John also helped start a nearby hospice for homeless women, which he placed under the protection of St. Aloysius Gonzaga - one of his favorite saints.
For many years, John avoided hearing confessions for fear he would have a seizure in the confessional, but the bishop of Civitá Castellana convinced him it was part of his vocation; he relented, and soon became one of the most sought after confessors in Rome. He worked tirelessly, spending many hours a day hearing confessions, particularly those of prisoners, the poor and illiterate in the hospitals or in their homes. He preached to them five and six times a day in churches, chapels convents, hospitals, barracks, and prison cells, so that he became known as "the apostle of the abandoned", a second Philip Neri.
John's frail health compelled him in 1763 to move to the Trinita dei Pellegrini, where he suffered a stroke that same year and received the last sacraments. He recovered enough to resume celebrating Mass, but, in 1764, he had another stroke and died at the age of 66. He was buried at the altar of the Blessed Virgin in the Church of Trinita de Pelleghrini. He was canonized by Pope Leo XIII on December 8,1881.
Patron of Corsica