He was a lawyer and politician, a mathematician and alchemist, an antiquarian, poet and friend of French literati.
D'Espagnet co-chaired De Lancre's 1609 repression, also congratulating his colleague on his job in the introduction to L'Incrédulité et mécréance du sortilège pleinement convaincues, besides condemning the Basque people, "this perverse people".
[3] Jean D'Espagnet is known to have owned several books that had previously formed part of Montaigne's library, including his copy of De rerum natura, in which his signature overwrites that of Montaigne's on the title-page.
[4] In 1623, D'Espagnet wrote Arcanum Hermeticae philosophiae and Enchiridion physicae restitutae.
[5] His son, Étienne d'Espagnet, utilised his father's library and designed optics for astronomy.