This short note aims at presenting an unpublished manuscript by Simone Assemani (1752-1821) containing the Italian translation of the life, in Arabic, of the Coptic saint Marqus al-Anṭūnī (1296-1386). This translation is particularly interesting as the manuscript on which Assemani based his work turns out to be seemingly the oldest copy known. Considering that a critical edition of the Arabic codex containing the Qiṣṣat ḥayāt al-qiddīs al-shaykh Marqus al-Anṭūnī is still lacking, and that the Italian translation by Assemani has just been re-discovered, it is possible now to work on a critical edition of the Arabic text and its translation using Assemani’s unpublished annotated text as a valuable, additional source.