<p>Two-dimensional (2D) photocatalysts offer significant potential for solar-driven water splitting; however, their practical application is often hindered by limited carrier mobility and suboptimal light absorption. In this work, we systematically explore the photocatalytic properties of monolayer ZnSnP₂S₆ through first-principles calculations and demonstrate its superior performance compared to conventional 2D materials. ZnSnP₂S₆ features an indirect band gap of 2.59&#xa0;eV and pronounced optical anisotropy, with strong absorption spanning the visible to ultraviolet regions. Notably, it exhibits ultrahigh electron mobility of up to 11,341.95&#xa0;cm²V⁻¹&#xa0;s⁻¹, significantly exceeding that of many well-known 2D photocatalysts. The conduction and valence band edges straddle the redox potential window for water splitting over a wide pH range (0–12), and the material shows low overpotentials for both hydrogen and oxygen evolution reactions. Combined with its favorable electronic, structural, thermal, and mechanical stability, monolayer ZnSnP₂S₆ emerges as a highly promising candidate for efficient 2D photocatalytic water splitting applications.</p> Graphical Abstract <p></p>