It has been generally accepted by modern scholars that al-Qāḍī al-Nu'mān was in the beginning either a Mālikī or a Ḥanafī and that he subsequently became an Imāmī and finally adopted the Ismā'īlī faith. The Imāmī savants, from al-Qāḍī Nūr Allāh Shūshtarī to Āghā Buzurg-i Tihrānī, maintain that al-Qāḍī al-Nu'mān was one of their co-religionists. Ismā'īlīs, on the other hand, regard him as one of the pillars of their da'wa. In the light of recently discovered sources and of the consequent revaluation and reinterpretation of earlier works, a re-examination of the question of al-Qāḍī al-Nu'mān's madhhab becomes necessary. The present article attempts to do precisely that, and show how and when the theory of al-Qāḍī al-Nu'mān's conversion originated.