We apply the difference-in-discontinuities design to disentangle the fiscal effects of the governance system conditional on electoral systems. We take advantage of a natural experiment, which involves two institutional reforms at the local level in Poland. The first reform introduced two electoral rules, which change along an exogenous population threshold: smaller municipalities use majoritarian elections, larger municipalities use proportional elections. The second reform changed the governance system in Polish municipalities from “parliamentary” to “presidential”. Our results indicate that a change from parliamentary to presidential form led to lower vertical fiscal imbalance predominantly in the jurisdictions with majoritarian elections and to a lesser extent in municipalities governed by proportional elections. This therefore confirms an interaction effect between the forms of government and electoral rules.