 He first practised as a physician and officiated as a Jewish preacher at Livorno, Italy.There he wrote in Italian a work entitled "Paschologia" (Cologne, 1702), in which he dealt with the differences of calculation in the calendars of the Greek, Roman, and Jewish churches, and demonstrated the errors which had crept into the calendar from the First Council of Nicaea until 1692.In 1702 Nieto succeeded Solomon Ayllon as ecclesiastical chief of the Portuguese Jews in London; and two years after his settlement in that city he published his theological treatise, "Della Divina Providencia, ó sea Naturalezza Universal, ó Natura Naturante" (London, 1704).