From Jewish origins, he therefore had to study in many universities and live in different cities and was never able to qualify for the positions that corresponded to his capacity, for which he demanded a statute of cleanliness of blood. He studied at La Bañeza and at the Colegio de Jesús de Monforte de Lemos; studied philosophy with the Dominican friars of the monastery of Trianos de Villamol and theology in Valladolid and Salamanca. In 1676 he was parish priest of Talavera de la Reina, in 1681 of Albares and in 1685 of Camarma de Esteruelas; destined to the capital, in 1697 it took charge of the church of San Pedro and in 1701 of the one of San Andres. He was confessor of Cardinal Portocarrero, synodal examiner of the archbishopric of Madrid and qualifier of the council of the Inquisition; Bishop Elect of Monopoli and Zamora, he resigned from both dioceses, probably because of his Jewish roots.
In 1713 he was one of the founders of the Royal Spanish Academy and in 1715 he was appointed senior librarian of the newly opened Royal Library, replacing the late Gabriel Álvarez de Toledo, a job he held until his death; He assembled to form the fund of what would be the future National Library, a great number of incunabula, rare and forbidden, many of them obtained abroad by mocking the census hand of the Inquisition, of which he himself was a part.
He left written a work in 16 volumes, Synopsis historical chronologica of Spain (1700-1727), in which he tells the history of Spain until the end of the sixteenth century; was translated into full French enriched with historical and critical notes under the title of Histoire Générale d’Espagne …
Blas Nasarre published an historical Elogio de Don Juan de Ferreras (Madrid: Printing of the Royal Spanish Academy, 1735).