Hey ! I'll give a try to this question !

The fact that the Mamluks sultans were former slaves was not considered, from a legal point of view, as an impediment to become Caliph, as they had been freed and thus were not considered as slaves anymore (which did not preclude that many people despised them because of their former status of slaves). Also, allow me to point here that quite a few “Mamluk sultans”, especially in the 14th century, were never slaves, and were never Mamluks (for example, the descendants of Sultan Qalâwûn, the Qalâwûnids, were born free). This most notably concerns al-Nâsir Muhammad, considered as one of the main ruler of the Mamluk sultanate. I just wanted to clarify this point because this image of the “Mamluk period” where all the military and political elites were “Mamluks” is an exaggeration, mainly due to academics themselves and past historiography of the field, but historians have now started to reconsider this framework.

Now to try to answer your question, one of the main reasons why the Mamluks could not become caliphs is that they initially supported the Abbasid family claims to the sultanate –as the Ayyûbid dynasty before them– and installed a member of the Abbasid family as Caliph in Cairo during Baybar’s rule (r. 1260-1277), after the fall of the Abbasid Caliphate in Baghdad in 1258. As such, the sultans of Syria and Egypt largely recognized the Caliphs belonging to the Abbasid family (the descendants of the Prophet’s uncle, Abbâs). Thus, the Abbasid were recognized as legitimate by the Mamluk sultans and their names were pronounced in the Friday sermon in the mosques within the domains of the Cairo sultanate/Mamluk sultanate. The fact that the Abbasid Caliphs of Cairo had no real power, except spiritual and symbolic (this symbolic importance being at times translated in the political stage), does not change the fact that they were recognized as caliphs.

By the time the “Mamluks” came to power, a kind of consensus had also emerged in the Middle East regarding the requirements to access the caliphate, which created another putative difficulty for the Mamluks to claim the title of Caliph. For several conditions were considered strictly necessary to assert such a claim: for example, being of legal age, being a free man, being a Muslim and other conditions (sight, bravery etc.). One of these conditions was: being a descendant of the Prophet Muḥammad’s tribe of Quraysh (a condition that Ottomans in the 16th century would contest, stating it only referred to the beginnings of Islam).

Therefore, there were theoretically two main issues regarding any putative claims of the Mamluk sultans to become caliphs: an Abbasid caliph was already living in the Mamluk capital, and enjoyed great fame, support from the local population, along with a long-standing and widely recognized and respected claim to the Caliphate, including outside the domains of the Cairo sultanate (namely, the “Mamluks” domains). The other issue was that the Mamluk sultans were not member of the tribe of Quraysh, a fact widely known at the time and not contested.

That being said, these requirements did not stop other rulers, elsewhere in the Islamic world around the same period, to claim the caliphal title (Almohads, Hafsid, Timurid etc.). At the end of the Mamluk period, the Mamluk Sultan Qânsûh al-Ghawrî (r. 1501-1516) did try to frame his rule as caliph, and was celebrated by members of his court as “Commander of the believers” and “Caliph of the Muslims”, traditional titles clearly referring to a Caliphal claim (See C. Mauder, In the Sultan’s Salon, 862–923).

So I guess, ultimately the reasons why the Mamluk did not declare themselves as Caliphs were linked to a variety of factors, including how they saw their political interests (better to keep the Abbasid Caliph in Cairo; M. Banister speaks of a “Mamluk reluctance” to break with the early successful strategy of the second half of the 13th century), how they framed their own legitimacy (including by demonstrating a proximity with the old Arab aristocracy, embodied by the Abbasid family), how they were perceived by the local population they ruled (especially the scholarly environment of Egypt and Syria). As M. Banister sums it up in his Ph. D. dissertation (sorry, do not have the book yet!): “Ideologically and theoretically, the Mamluks behaved as though the caliphs were indispensable to the maintenance and functioning of the regime throughout the span of their sultanate” (The Abbasid Caliphate of Cairo, p. 495).

I hope this helps !

Bibliogaphy used for this comment

Hugh Kennedy, The Caliphate (London: Penguin, 2016)
M. Banister, The Abbasid Caliphate of Cairo (1261-1517): History and Tradition in the Mamluk Court (ph. Dissertation, University of Toronto, 2015).

Christian Mauder, In the Sultan’s Salon: Learning, Religion, and Rulership at the Mamluk Court of Qāniṣawh al-Ghawrī (r. 1501–1516) (Leiden: Brill, 2021), 862–923.

M. Banister, The Abbasid Caliphate of Cairo, 1261-1517: Out of the Shadows (Edinburgh: Edinburgh University Press, 2021).