As official representatives of governments, ambassadors are charged with prevent-ing conflict and fostering cooperation. They are also empowered to promote the se-curity and economic interests of their home states, including by increasing exportsand facilitating cooperative trade outcomes. As such, during ambassadorial vacan-cies, diplomatic influence – and the associated commercial cooperation – is likely towane. We evaluate this theory by tracing the impact of US ambassadorial vacancieson bilateral international trade. Leveraging high-frequency and plausibly exogenousvariation in vacancies associated with the timing of US Presidential inaugurations, weshow that periods of US ambassadorial vacancies reduce US exports, but do not affectUS imports. These findings are driven by the vacancies of career diplomats, and aremagnified in poorer countries, where the lower quality of institutions and regulationsmake the information exchange and commitment mechanisms that diplomats provideeven more vital. One first contribution to the existing research comes from using fine-grained monthly-level and product-level data (whereas previous research has used onlyaggregated annual flows). Our second contribution is that we test the specific causalmechanisms through which diplomats influence trade flows. Our findings demonstratethe conditions under which and channels through which diplomacy can affect bilat-eral trade flows, adding to the burgeoning literature on the role of ambassadors inpromoting commercial cooperation.