Scholars and pundits have long debated whether religion helps new immigrants integrate politically in the United States. Those who see religion as an integrative institution cite the country’s history of vibrant religious congregationalism that supports connections between the native and foreign born, while critics point to anti-immigrant hostility, Christian nationalism, and patterns of religious membership that can reinforce social segregation. This article aims to adjudicate this debate, using a large sample of survey data, the New Immigrant Survey (NIS), fielded among new legal residents in 2003/2004. I find that religious membership is associated with increased probability of naturalizing in a short (3.5–7 years) timeframe and is stronger for those with greater human capital and income and longer tenure in the United States. Involvement in US-origin congregations also exhibits a stronger effect on naturalization than involvement in national-origin congregations. Additionally, I find that religious minorities, though less likely to be members of congregations, are independently more likely than Christian immigrants to naturalize in the same timeframe. These results are interpreted as support for a view of organized religion as a setting for American identity formation and a basis for mobilizing resources in response to anti-immigrant sentiment. For certain groups, organized religion seems to support a type of selective acculturation that combines American citizenship with the establishment and/or retention of a distinct ethno-religious identity. The article thus affirms, with caveats, the broader relevance of a long tradition of ethnographic scholarship on immigrant religion in the United States.