Born in Ghent, Belgium of Catholic Flemish stock, Henri Lammens joined the Society of Jesus in Beirut at the age of fifteen, and settled permanently in Lebanon. During his first eight years there Lammens mastered the Arabic language, as well as Latin, and Greek. His first work of scholarship was a dictionary of Arabic usage (1889). He edited al-Bashir, the Jesuit newspaper of Beirut, and after much travelling, he began his career as an Orientalist at the School of Oriental Studies at the Jesuit College in 1907.
He published a series of studies on the Umayyads, and several on pre-Islamic Arabia: Etudes sur le regne du calife Omaiyade Mo'awia ler (1908), Le berceau de l'Islam; L'Arabie occidentale à la vielle de l'Hegire (1914). He contributed many articles to the first edition of the Encyclopaedia of Islam, as well as to various learned journals.
His contributions are considered highly influential among Western historians of Islam; and yet he has often been criticized for his skewed portrayal of many issues. It is universally acknowledged "that Lammens provided the study of the sira with a new basis; and none would underestimate his contributions on the history of the Umayyads."
Franz Buhl remarks: «dessen Belesenheit und Scharfsinn man bewundern muss, der aber doch oft die Objektivität des unparteiischen Historiker vermissen lässt.» Des Leben Muhammeds, p. 367.
i.e. "One must admire his [Lammens'] erudition and acumen, which however do not often admit of the objectivity of an impartial historian."
A Library Journal reviewer wrote: