He learned Latin and Greek at Rochelle, and continued his studies in Leiden, subsequently moving to Paris. His conversion to the Roman Church is ascribed to Cardinal du Perron. In 1618 he joined the congregation of the Oratory, and in due course took priest's orders. In 1625 he visited England in the train of Henrietta Maria; in 1640 he was at Rome, on the invitation of Cardinal Barberini, and was received with special favor by Pope Urban VIII. He was, however, soon recalled to Paris by Richelieu, and the rest of his life was spent in incessant literary labor. The Histoire de la delivrance de elglise chretienne par l'emp. Constantin, et de la grandeur et souverainettern porelle donne a elglise romaine par les rois de France (1630) gave great offence at Rome, and a Declaration (1654), directed against faults in the administration of the Oratory, was strictly suppressed.
Morin's chief fame rests on his biblical and critical work. By his editing of the Samaritan Pentateuch and Targum, in the Paris Polyglott, he gave the first impulse in Europe to the study of this dialect, which he acquired without a teacher (framing a grammar for himself) by the study of MSS. then newly brought to Europe. Not unnaturally, he formed a very exaggerated view of the value of the Samaritan tradition of the text (Exercitationes in utrumque Sainaritanorum Pentateuchum, 1631). A similar tone of exaggerated depreciation of the Masoretic Hebrew text, colored by polemical bias against Protestantism, mars his greatest work, the posthumous Exercitationes biblicae de hebraeici graecique textus sinceritate (1660), in which, following in the footsteps of Cappellus, but with incomparably greater learning, he brings irrefragable arguments against the then current theory of the absolute integrity of the Hebrew text and the antiquity of the vowel points.