In water-splitting catalysts, exposing high-activity crystal facets with optimal electronic structures can significantly enhance the oxygen evolution reaction (OER) kinetics. In this work, we demonstrate a facile strategy for simultaneously modulating the preferential crystal facet and electronic structure of perovskite oxides for their use as water-electrolysis catalysts using a template-mediated growth approach. Experimental and computational analyses revealed that the preferred crystal facet of La_0.5Sr_0.5CoO₃ (LSC) grown on MoReS₂ was effectively modulated to the (110) plane, and the free energy barrier of the rate-determining step was lowered by such crystal facet engineering. Furthermore, the interfacial charge transfer between LSC and MoReS₂ enabled the optimal electronic structure of the B-site cation in LSC. Consequently, LSC grown on MoReS₂ exhibited an OER activity of 210 mV at 10 mA cm^–2, surpassing the performance of state-of-the-art perovskite oxide-based catalysts. Our findings provide new insights into the design of efficient perovskite oxide-based electrocatalysts for water electrolysis.