Taking an approach from religion as a social identity and using large-scale comparative surveys in five European cities, we investigate when and how perceived discrimination is associated with religious identification and politicization among the second generation of Turkish and Moroccan Muslims. We distinguish support for political Islam from political action as distinct forms of politicization. In addition, we test the mediating role of religious identification in processes of politicization. Study 1 estimates multi-group structural equation models of support for political Islam in Belgium, the Netherlands, and Sweden. In line with a social identity model of politicization and across nine inter-group contexts, Muslims who perceived more discrimination identified (even) more strongly as Muslims; and high Muslim identifiers were most ready to support political Islam. In support of a competing social stigma hypothesis, however, negative direct and total effects of perceived discrimination suggest predominant depoliticization. Using separate sub-samples across four inter-group contexts in Belgium, Study 2 adds political action tendencies as a distinct form of politicization. Whereas religious identification positively predicts both forms of politicization, perceived discrimination has differential effects: Muslims who perceived more discrimination were more weary of supporting political Islam, yet more ready to engage in political action to defend Islamic values. Taken together, the studies reveal that some Muslim citizens will politicize and others will depoliticize in the face of discrimination as a function of their religious identification and of prevailing forms of politicization.