The son of a Protestant minister who had converted to Catholicism (although the House of Astruc was of medieval Jewish origin), Astruc was educated at Montpellier, one of the great schools of medicine in early modern Europe. His dissertation and first publication, submitted when he was only 19, is on decomposition, and contains many references to recent research on the lungs by Thomas Willis and Robert Boyle. After teaching medicine at Montpellier he became a member of the medical faculty at the University of Paris. His numerous medical writings, or materials for the history of medical education at Montpellier, are now forgotten, but the work published by him anonymously in 1753 has secured for him a permanent reputation. This book, brought out anonymously in 1753, was entitled Conjectures sur les mémoires originauz don't il paroit que Moyse s'est servi pour composer le livre de la Génèse. Avec des remarques qui appuient ou qui éclaircissent ces conjectures ("Conjectures on the original documents that Moses appears to have used in composing the Book of Genesis. With remarks that support or throw light upon these conjectures"). The title cautiously gives the place of publication as Brussels, safely beyond the reach of French authorities. Not all the 18th century books that declare that they were printed at Amsterdam or Geneva, to cite two other familiar imprints, were actually printed outside France. It was a safeguard.

Indeed a safeguard was required. The forcible "re-Catholicization" of Astruc's Languedoc homeland in the frame of the Counter Reformation, when the Protestant "Camisards" were being deported or sent to the galleys, was a very recent memory. In Astruc's own times the writers of the Encyclopédie were working under great pressure and in secret, for Catholic Church did not offer a tolerant atmosphere for biblical criticism. This was somewhat ironic, for Astruc saw himself as fundamentally a supporter of orthodoxy; his unorthodoxy lay not in denying Mosaic authorship of Genesis, but in his defence of it. In the previous century scholars such as Thomas Hobbes and Baruch Spinoza had drawn up long lists of inconsistencies and contradictions and anachronisms in the Torah, and used these to argue that Moses could not have been the author of the entire five books. Astruc was outraged by this "sickness of the last century", and determined to use modern 18th century scholarship to refute that of the 17th. Using methods already well established in the study of the Classics for sifting and assessing differing manuscripts, he drew up parallel columns and assigned verses to each of them according to what he had noted as the defining features of the text of Genesis: whether a verse used the term "YHWH" (Yahweh) or the term "Elohim" (God) referring to God, and whether it had a doublet (another telling of the same incident, as for example the two accounts of the creation of man, and the two accounts of Sarah being taken by a foreign king). Astruc found four documents in Genesis, which he arranged in four columns, declaring that this was how Moses had originally written his book, in the image of the four Gospels of the New Testament, and that a later writer had combined them into a single work, creating the repetitions and inconsistencies which Hobbes, Spinoza and others had noted.

Astruc's work was taken up by a succession of German scholars, the intellectual climate in Germany then being more conducive to scholarly freedom, and in their hands formed the foundation of modern critical exegisis of the Old and New Testaments.