After a short stay at Florence as tutor for a noble family, and as judge of sorcerers, he was received into the Order of Friars Minor, in the chapel of the Portiuncula, in Assisi, on 26 July 1416.

Having finished his novitiate at the hermitage of the Carceri, near Assisi, he studied theology at Fiesole, near Florence, with John of Capistrano,[2] under Bernardine of Siena.

[2] On 13 June 1420, he was ordained a priest and soon began to preach in Tuscany, in the Marches, and in Umbria; for half a century he carried on his spiritual labours, remarkable for the miracles he performed and the numerous conversions he wrought.

[2] From 1427, James preached penance, combated heretics, and was on legations in Germany, Austria, Sweden, Denmark, Bohemia, Poland, Hungary, and Bosnia.

[5] He combated the heresies that he found there, which earned him the hostility of its ruler, King Tvrtko II, and even more of his wife, Queen Dorothea, whom James accused of trying to poison him.

[8] He instituted several montes pietatis (literally, "mountains of piety": nonprofit credit organizations that lent money at very low rates on pawned objects), and preached in all the greater cities.

A few years later, on Easter Monday 1462, James, preaching at Brescia, uttered the opinion of some theologians that the Precious Blood shed during the Passion was not united with the Divinity of Christ during the three days of his burial.

On his notebook, or "Itinerarium", See Luigi Tasso in "Miscellanea Francescana", I (1886), 125-26: "Regula confitendi peccata" was several times edited in Latin and Italian during the fifteenth century.

At the instigation of the provincial minister (Franciscan superior) of the Marches region, Ferdinando Campana, James's body was relocated to Monteprandone, where it remains incorrupt and visible to the public today.

He is generally represented holding in his right hand a chalice, out of which a snake is escaping – an allusion to some endeavours of heretics to poison him or, less likely, to the controversy about the Precious Blood.