Objective This study (1) introduces a new framework to conceptualize and measure political Islam, and (2) examines the empirical nexus among Islamic religiosity, ideological support for political Islam (ISPI), and collective protests in the Arab Middle East. Methods Analyzing cross‐national attitudes in five Arab states, I conduct a principal component analysis to construct a new index to account for a variation in ISPI, and examine the effects thereof on participation in collective protests. Results The evidence shows that Islamic religiosity matters in challenging political elites via collective action. While politically moderate Muslims appear more likely to engage in nonviolent, collective political protests, political radicals seem less likely to do so. Conclusion The findings suggest that political ideology plays a central role in moderating the intricate relationship between Islam and collective political activism. The evidence also supports the resource mobilization thesis, among other factors, to explain the dynamics of collective action in the Arab world.