Fromondus was born in Haccourt sur Meuse, Belgium, near Liège, and was educated in humanities at the Jesuit college in Liège. He left in 1604 to study philosophy and languages at the Collège de Faucon in Louvain; there he befriended a Dutch student, Cornelius Jansen of Acquoy, the future Jansenius. Fromondus then taught philosophy at the Abbey Saint-Michel in Anvers. He returned to Louvain in 1609, where he taught rhetoric (1609–14) and philosophy (1614–28), while pursuing the scientific interests that led to the publication of several astronomical treatises; these included the astronomical fantasy Coenae saturnalitiae, variatiae Somnio sive Peregrinatione coelesti (1616), Dissertatio de cometa anni 1618 (1619), and Meterologicum libri VI (1627). In the latter two treatises, Fromondus argued against Aristotle (and in the Meteors also against Galileo) that comets are superlunary phenomena. In the 1620s, he resumed his studies in theology under Cornelius Jansen (with whom he would remain closely associated) and obtained a doctorate in theology in 1628. He published in this period, among other works, Labyrinthus sive de compositione continui, a defense of Aristotle and attack on atomism (1631), and Ant-Aristarchus sive Orbis terræ immobilis, a critique on the work of the Dutch Copernican Philip van Lansbergen (1631); Jacob Lansbergen replied with Apologia … (1633), a defense of his father's work, and Fromondus replied with Vesta, sive Ant-Aristarchi vindex (1634). When Jansenius was appointed bishop of Ypres in 1636, Fromondus assumed his chair as professor of Sacred Scripture. During his fatal illness in 1638, Jansenius entrusted the manuscript of his Augustinus to Fromondus, who arranged for its publication in 1640. Fromondus subsequently published several theological works in defense of Jansenism. He died in 1653 in Louvain.

Fromondus was one of the small circle of savants to whom Descartes sent a copy of his Discourse on Method. Fromondus replied by sending to Descartes his Labyrinthus sive de compositione continui, his tract against Epicureans and atomists, and provided him with a series of objections against what he saw as Descartes’ overreliance on atomistic and mechanical principles. Concerning Descartes’ account of body in the Meteors, Fromondus commented: “This composition of bodies made up of parts with different shapes … by which they cohere among themselves as if by little hooks, seems excessively crass and mechanical” (AT I 406). Descartes clearly respected Fromondus, although he thought him too philosophically conservative. His attitude toward his critic nevertheless remained cordial. In a 1638 letter, Descartes explained that his disagreement with Fromondus was “conducted like a chess game: we remained good friends after the match was over, and now we send each other nothing but compliments” (AT II 660).

See also Atom; Body; Jansenism; Plempius, Vopiscus Fortunatus