The issues of migration and immigrant political integration in western democracies have become increasingly intertwined with debates on religion, particularly Islam. To date, however, we have surprisingly little systematic research on how religious beliefs are related to immigrants’ political engagement. In this study, we argue that religion has a capacity to mobilize immigrants politically but the strength of this relationship depends on immigrant generation, religiosity, and the type of religion. Using survey data collected as part of the European Social Survey (ESS) 2002–2010 in 18 West European democracies, our analyses reveal that religion is indeed linked to political engagement of immigrants in a complex way: while belonging to a religion is generally associated with less political participation, exposure to religious institutions appears to have the opposite effect. Moreover, we find that, compared to foreign-born Muslims, second-generation Muslim immigrants are not only more religious and more politically dissatisfied with their host countries, but also that religiosity is more strongly linked to their political engagement. This relationship, however, is limited to uninstitutionalized political action.