This dissertation explores laywomen's contributions in four key areas of U.S. Catholic history during the nineteenth century. Beginning in the 1850s, laywomen worked to convince European women religious to establish new communities in the United States, and raised money to support them. By the 1870s and 1880s, prominent laywomen were engaged in fierce battles to defend Catholic educational institutions from perceived government attacks. Particularly in light of their service during the Civil War, Catholics believed they had effectively demonstrated their patriotism, but continued to find ways to showcase Catholic contributions to U.S. history into the 1890s. They also endeavored to shape the U.S. Church's relationship with Rome from mid-century well past 1900.The project makes three significant historical interventions. First, it argues that by examining numerous thematic aspects of laywomen's involvement in nineteenth-century U.S. Catholic history (namely, supporting religious orders, defending Catholic institutions, engaging in civic causes, and gaining access at Rome) we can see how laywomen—particularly elite, native-born women—have not only had agency, but power, within the Catholic Church. Second, by featuring laywomen as protagonists, the project demonstrates that the transnational turn in U.S. Catholic history need not be defined by clergy, religious orders, or the longstanding "immigrant paradigm" long dominant in the field. Finally, it shows how influential laywomen, freed from being labeled "foreign" or "illiberal" by virtue of their social status and powerful networks, inserted their voices within public debates about "America" and "Americanness" during the long nineteenth century.