One of four children born to Charles de Rossi and Frances Anfossi. Taken by a wealthy noble couple to Genoa, Italy for schooling. There he met some Capuchin friars who thought well of him, and helped him continue his education in Rome, Italy. Studied under the Jesuits at the Roman College at age 13. Member of the Sodality of the Blessed Virgin and the Ristretto of the Twelve Apostles. Epileptic.
His self-imposed acts of austerity nearly broke his health, and he never completely regained his strength. Studied philosophy and theology under the Dominicans. Ordained on 3 March 1721, assigned to Rome.
Helped start a hospice for homeless women near Saint Galla’s hospice in Rome. Canon of Santa Maria, Cosmedin in 1737; he used his compensation from the position to purchase an organ for the church. Missioner and catechist to the teamsters, farmers, herdsmen, homeless, sick, beggars, prostitutes, and prisoners of the Campagna region. For many years, John was 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. John relented, and soon became a sought after confessor in Rome; he once said that the shortest road to heaven was to guide others there by the confessional. Sought after preacher. Assigned as catechist to many government and prison officials, including the public hangman. Miracle worker. Always had a special devotion to Saint Aloysius Gonzaga