Cappel, a Huguenot, was born at St Elier, near Sedan. He studied theology at Sedan and Saumur; and Arabic at the University of Oxford, where he spent two years. At the age of twenty-eight he accepted the chair of Hebrew at Saumur, and twenty years later was appointed professor of theology. Amongst his fellow lecturers were Moses Amyraut and Josué de la Place.
As a Hebrew scholar he made a special study of the history of the Hebrew text, which led him to the conclusion that the vowel points and accents are not an original part of the Hebrew language, but had been inserted by the Massorete Jews of Tiberias, no earlier than the 5th century; he also concluded that the primitive Hebrew characters are those now known as the Samaritan, while the square characters are Aramaic and were substituted for the more ancient at the time of the captivity. These conclusions were hotly contested by Johannes Buxtorf, since they conflicted with those of his father, Johannes Buxtorf senior; Elias Levita had already disputed the antiquity of the vowel points and neither Jerome nor the Talmud showed any acquaintance with them.
Cappel's second important work, Critica Sacri, was distasteful, from a theological point of view. He had completed it in 1634; but fierce opposition prevented him from printing it at Paris until 1650. The various readings in the Old Testament text and the differences between the ancient versions and the Massoretic text convinced him that the idea of the integrity of the Hebrew text, as commonly held by Protestants, was untenable. This amounted to an attack on the verbal inspiration of Scripture. Bitter, however, as was the opposition to his views, it was not long before his results were accepted by scholars.
Cappel was also the author of Annotationes et Commentarii in Vetus Testamentum, Chronologia Sacra, and other biblical works, as well as of several other treatises on Hebrew, among which are the Arcanum Punctuationis revelatum (1624) and the Diatribe de veris et antiquis Ebraeorum literis (1645). His Commentarius de Capellorum gente, giving an account of the family to which he belonged, was published by his nephew James Cappel (1639-1722), who, at the age of eighteen, became professor of Hebrew at Saumur, but, on the revocation of the edict of Nantes, fled to England. See Herzog-Hauck, Realencykiopädie.