Much existing research on Islamist political parties and their supporters in the Middle East has focused on an Islamist/non-Islamist distinction within primarily Sunni Muslim communities, while framing ostensibly Islamist Shi‘a parties and movements primarily as in terms of sectarian attachments rather than beliefs on the role of religion in politics. This paper challenges this framing through a cross-national and cross-sect comparison of individual attitudes towards political Islam and nominally Islamist parties in the Arab world, as expressed in Wave III of the Arab Barometer. Such analysis finds little sign of a uniform division between Sunni and Shi’a respondents within countries, let alone an overarching set of views shared across country contexts—there is no clear basis for excluding Shi‘a Muslims from investigations of “Islamism” writ large. On the other hand, the paper finds that a relatively homogenous “ideal-type” of Sunni Muslim support for Islamist parties does not travel to multi-sectarian contexts, even for political parties that meet mainstream definitions of “Islamists.” We offer three recommendations on the basis of these findings. First, and at a minimum, work based on Sunni Islamist parties should acknowledge potential sect-specific scope conditions. Second, comparative work incorporating Shi‘a-Islamist cases can generate new theories of how Islamists gain and exercise power by highlighting explanatory factors common to Sunni and Shi‘a contexts alike. Finally, bringing “the other Islamists” back in holds the potential to reimagine the study of Islamism to better integrate findings from this subfield into the study of religious and identity-based political parties and movements.