When he was about forty-five years of age, he made his solemn profession in the Order of Friars Preachers, and drilled himself like a recruit, in the exercise of every virtue, but, above all, in charity to the poor, and mainly to the captives taken by the infidels. It was by his exhortation that St. Peter Nolasco (who was his penitent) was induced to devote all his riches to this most pious work. The most blessed Virgin appeared to Peter, as also to blessed Raymund and to James I, King of Aragon, telling them, that it would be most pleasing to herself and her only Son, if in their honour an Order of religious men were founded, whose mission would be to deliver captives from the tyranny of the infidels. Whereupon, after deliberating together, they founded the Order of our Lady of Mercy for the Ransom of Captives; and blessed Raymund drew up certain rules of life, well adapted to the vocation of that order. Some years after, he obtained their approbation from Gregory the Ninth, and made St. Peter to whom he gave the habit with his own hands, first general of the order.
He was summoned to Rome by Gregory IX, and appointed his Chaplain, Penitentiary, and Confessor. It was by Gregory's orders that he collected, in the volume called the Decretals, the ordinances of the Roman Pontiffs, which up to that time were only to be found scattered among the records of various Councils and Churches. He firmly refused the Archbishopric of Tarragona, which was offered to him by the Pope himself, and having been chosen Master General of the whole order of Friars Preachers, he discharged the duties of that office in holiness for two years, and then resigned it. It was by his advice that James, King of Aragon, established the Office of the Holy Inquisition in his dominions. He was distinguished by many miracles, of which the chief was that, when returning to Barcelona from the Island of Majorca, he spread his cloak upon the sea, and passed over the waters upon it, accomplishing the whole distance of an hundred and sixty miles in six hours, and finally entering his convent through closed doors. He attained the age of nearly an hundred years, and fell asleep in the Lord in the year of salvation 1275. His name was enrolled by Clement VIII among those of the Saints.