He converted to Christianity in 1601 in Feuchtwangen, and wrote Jüdischer Abgestreifter Schlangenbalg (The Jewish Serpent's Skin Stripped), in which he bitterly attacked his former coreligionists, whom he accused of hating "the most pious and innocent Jew, Jesus Christ," and in which he denounced their religious literature.
Solomon Ẓebi Hirsch of Aufhausen wrote a response in Yiddish, Yudisher teryak (The Jewish Antidote; Hanau, 1615), countering Brenz' accusations.
A new edition appeared in Altdorf in 1680, and a Latin translation by Johann Wülfer, together with the Schlangenbalg, was published in Nuremberg in 1681.
Wülfer strongly defended the Jews against Brenz, criticising him for the plagiarism of Johannes Pfefferkorn that he exposed.
A Hebrew translation under the title Ha-Yehudim, by Alexander ben Samuel, is extant in manuscript in the library of the University of Leyden.