Does electoral integrity improve local development? While prevailing theories suggest that clean elections and accountability drive development, alternative perspectives propose that clientelistic networks can also serve as governance channels. In this paper, we address this question causally by analyzing data from an original RCT conducted during Colombia’s 2019 local mayoral elections, designed to promote electoral integrity. Leveraging the intervention’s effect on increasing the likelihood of electing cleaner candidates as a “first stage,” we assess the impact of electoral integrity on municipal development. Our findings indicate that, four years after the intervention, municipalities with better electoral integrity exhibit higher rates of citizen access to public goods and services. To explore the mechanisms behind these results, we show that mayors elected in intervention areas do not differ significantly in public sector experience, incumbency, or sociodemographic characteristics, suggesting that selection effects are unlikely to explain the observed differences. We also find no increase in demand for public goods in these municipalities, implying that the observed effects arise from the supply side. Additionally, mayors in intervention areas are less likely to be investigated or sanctioned by Colombian oversight agencies, suggesting reduced rent-seeking behavior among these officials. Lastly, we document that citizen monitoring of elections remains high in municipalities affected by the intervention, even four years post-intervention. Together, our findings provide the first causal evidence that improved electoral integrity strengthens accountability mechanisms in the medium term, prompting mayors to deliver more effectively on public goods and services.