Understanding electrified solid–liquid interfaces is critical to advancing electrochemical energy conversion, storage, and environmental remediation technologies. In this work, we employ constant‑potential grand‑canonical density functional theory (GC‑DFT) coupled with a hybrid implicit–explicit solvation scheme to probe the fundamental behavior of diverse electrified interfaces. We demonstrate the capability of this framework through applications to Pt(111)/water, graphene/water, and RuO₂(110)/water systems. By capturing the voltage‑dependent response of the electric double layer, our approach reconciles longstanding inconsistencies between conventional vacuum‑level DFT predictions and experimental measurements. This methodology provides a robust, predictive foundation for the rational design of next‑generation electrocatalysts, energy‑storage materials, and environmentally relevant electrochemical systems, enabling deeper insight into the complex physics that govern electrified interfaces.