Over a century ago, Horace Plunkett began a debate about the role of religion in Irish development, pointing to what he saw as the economic shortcomings of Roman Catholicism. Thereafter, however, the debate waned, and only limited scholarship has subsequently investigated the significance of religion in Irish development, especially in statistical terms. In this article that lacuna is addressed, using a quantitative approach to examine the relationship between Roman Catholicism and economic and financial development in the post-Famine era. Attention is directed to a variety of development indicators, namely, education, occupations, and commerce. By focusing on a selection of measures over time, it is possible to determine more precisely where differences, if any, occurred between the denominations and whether such differences changed over the period. The analysis reveals that Roman Catholicism tends to be initially negatively associated with more advanced development outcomes, but that this association weakens over time. As such, the results point to an economic convergence between Roman Catholics and Protestants, complementing historical evidence on an upward Catholic socioeconomic transition—a ‘Catholic embourgeoisement’—in the post-Famine era.