Rabbi Yosef Ergas was born in Livorno in 5445 (1685). His father, Rabbi Emanuel, was rabbi of the community; his maternal grandfather, Moses Pinheiro, had been a devoted follower of Shabbatai Tzvi. At eighteen he married the daughter of his mother's sister, who bore him three sons and three daughters.

He studied in the yeshiva of Rabbi Shmuel de Paz in Livorno and became known for his brilliance at a young age. He studied Kabbalah for seven weeks with Rabbi Binyamin HaKohen Vitale, a student of Rabbi Moshe Zacuto.

He later settled in Pisa, where he founded the Neveh Shalom yeshiva and two charities, Mohar HaBetulot and Malbish Arumim. Returning to Livorno, he was appointed rabbi of the community. Rabbis from Italy and France sent him their questions, which he answered clearly and concisely. His foremost student was Rabbi Malachi HaKohen, author of Yad Malachi. A determined opponent of Sabbateanism, in 1710 he expelled Nehemiah Chayon from Livorno when Chayon sought his approbation, and answered him with two polemical works printed in London in 1715, Tochachat Megulah and HaTzad Nachash.

Works: Shomer Emunim, a dialogue between a Talmudist and a Kabbalist, a foundational text and the leading statement of the non-literal view of tzimtzum, often called Shomer Emunim HaKadmon to distinguish it from the work of Rabbi Aharon Roth; Mevo Petachim, an introduction and rules for the writings of the Arizal; Divrei Yosef, sixty-eight responsa; and Minchat Yosef.

He passed away in Livorno on 3 Sivan 5490 (May 19, 1730), at the age of forty-five, and was buried there.