ABSTRACT What explains electoral support for Islamist parties? Existing literature assesses the role of programmatic appeals, in the form of religious ideology and economic programs, but lacks the data needed to test the role of particularistic benefits in shaping voter choice. Drawing on an original survey of 1,202 Tunisians conducted in 2012, I test the role of programmatic and particularistic benefits in explaining voter choice in Tunisia’s 2011 Constituent Assembly and 2014 parliamentary elections. I argue that, due to its greater party organizational capacity, Ennahda provided more constituency service than other parties and was more successful in attracting new supporters by 2012 as a result. In 2011, Ennahda voters were more religious and economically marginalized than non-Islamist voters. Yet by 2012, Ennahda developed a voter base drawn both from those who are ideologically committed to its religious program as well as those who requested constituency service from an Ennahda member. By showing that programmatic and particularistic appeals explain voter support for Islamist parties, this research extends the literature on Islam and politics and illustrates the importance of party capacity for developing a voter base in transitional contexts.