Developing low‐cost and industrially viable electrode materials for efficient water‐splitting performance and constructing intrinsically active materials with abundant active sites is still challenging. In this study, a self‐supported porous network Ni(OH)2‐CeOx heterostructure layer on a FeOOH‐modified Ni‐mesh (NiCe/Fe@NM) electrode is successfully prepared by a facile, scalable two‐electrode electrodeposition strategy for overall alkaline water splitting. The optimized NiCe0.05/Fe@NM catalyst reaches a current density of 100 mA cm−2 at an overpotential of 163 and 262 mV for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively, in 1.0 m KOH with excellent stability. Additionally, NiCe0.05/Fe@NM demonstrates exceptional HER performance in alkaline seawater, requiring only 148 mV overpotential at 100 mA cm−2. Under real water splitting conditions, NiCe0.05/Fe@NM requires only 1.701 V to achieve 100 mA cm−2 with robust stability over 1000 h in an alkaline medium. The remarkable water‐splitting performance and stability of the NiCe0.05/Fe@NM catalyst result from a synergistic combination of factors, including well‐optimized surface and electronic structures facilitated by an optimal Ce ratio, rapid reaction kinetics, a superhydrophilic/superaerophobic interface, and enhanced intrinsic catalytic activity. This study presents a simple two‐electrode electrodeposition method for the scalable production of self‐supported electrocatalysts, paving the way for their practical application in industrial water‐splitting processes.