Corruption undermines institutional integrity, erodes trust, and threatens cooperation—yet most evidence on its social consequences stems from correlational studies in WEIRD populations. This project introduces a global experimental framework to examine how institutional corruption shapes trust and cooperation across cultures. We adapted a paradigm introduced in recent work to operationalize institutional representatives as third-party punishers (TPPs). Corruption was manipulated by varying (dis-)honesty levels of TPPs, which were previously obtained in a die-rolling task that rewarded self-serving behavior at the expense of the collective. This study is pre-registered, incentivized, and free from deception. Data was collected from 13,536 participants across 34 societies selected to maximize their variation in institutional corruption levels, rule of law, and other relevant cultural dimensions. Across societies, the presence and integrity of TPPs systematically shaped cooperation, trust, and expectations. Cooperation and trust were highest in the presence of honest TPPs, and corruption at the societal level moderated these effects. This project highlights the value of large-scale controlled experimental approaches in cross-cultural social psychology and offers practical insights into the conditions under which institutions may or may not undermine cooperation globally.