This article analyses the participation of individuals, networks and international organizations in transnational fundraising aimed at providing humanitarian relief aid. Focusing on fundraising campaigns organized in the Italian states in favour of Ireland in 1847, when the Great Famine scourged its population the most, the article highlights the agency of the fundraisers in setting in motion an economy of altruism that transcended groups’ boundaries and state borders. The activism and networking of a few well-established individuals in Rome were pivotal in mobilizing the lay and religious elites at a local level. In January and February 1847, the elites of the Italian capitals collected copious sums within private events and initiatives directed at their peers, while the Christian faiths present in Rome organized the first alms collections. This wave of altruism succeeded in setting humanitarian relief for Ireland as one of the goals of the global Catholic Church. In March, Pope Pius IX issued the Encyclical Praedecessores Nostros, appealing for Catholics to donate in favour of Ireland, and thereby generating much local fundraising, mainly in the Italian states and Southern Europe, until the early months of 1848. The Catholic clergy served the cause, raising money locally and taking charge of its delivery to Ireland, with partial coordination from Rome. Although implementing a transnational fundraising campaign involved obstacles of a political, logistical and financial nature, the alms collection raised in the Catholic churches aggregated many small donations over a considerable time span, providing more than double the amount raised in the lay initiatives organized by the elites of the Italian states. The article, based on unedited archival sources from the Italian, Vatican and Irish archives, shows how the charitable fundraisers overcame the obstacles imposed by state politics, international conflicts and transaction costs over the transnational circulation of ideas, initiatives and capitals.