Grelot studied at St. Louis School, in Montargis. He was ordained a Catholic priest in 1941. He became a teacher at the Seminary of Orléans and afterwards at the Institut Catholique de Paris, from 1961 to 1983. He became an honorary teacher of the Institute in 1985.[citation needed]
He presented his thesis in theology, Èxègese Littérale, Éxègese Spirituelle ("Literal Exegesis, Spiritual Exegesis"), in 1949. He had an important role in the renewal of the Biblical studies in France with his books, Introduction aux Livres Saints ("Introduction to the Holy Books", 1954) and Pages Bibliques ("Biblical Pages", 1954), which were reissued several times and had translations in several different languages.[citation needed]
He had controversies with other biblical scholars who opposed a late dating of the New Testament writings; he wrote his book L'origine des Évangiles (1985) in opposition to the view held by Jean Carmignac.[2]