Literature on Islam and politics debates why Islamist parties succeed electorally, but one strand of this literature argues that it is due to service provision to economically marginalized or middle class citizens. Other research in Morocco and Tunisia shows that female citizens, who are one marginalized group, are more able to obtain services from Islamist than non-Islamist parties. Yet, the number of cases that have been examined is limited and a comparative framework is needed to understand whether, why, and under what conditions service provision to the poor supports Islamists’ electoral success. We address this question by drawing on original 2012 surveys of 40 Tunisian members and 2,422 citizens and find that electing members of the Islamist Ennahda party increases the likelihood that the poor know deputies’ names and request services. We attribute better symbolic and service responsiveness to an “Islamic mandate effect”—Islamist parties’ greater service provision institutionalization and mandate to serve marginalized communities. Our results extend literature on Islam and governance by illustrating that party institutionalization helps improve service provision to the poor and is part of the explanation for why Islamists success electorally