Photocatalysis offers a sustainable solution for essential reactions such as CO2 conversion and water splitting, but constraints in catalyst properties like bandgap and active site availability often limit its efficiency. High-entropy oxides (HEOs), which incorporate five or more different cations, present significant potential for this application due to their elemental diversity. This study explores active HEO development for photocatalytic applications by integrating cations with d0 and d10 electronic configurations. A single-phase HEO with a monoclinic structure was successfully synthesized, comprising elements with d0 (titanium, zirconium, niobium and tantalum) and d10 (zinc) electronic configurations. Comprehensive analyses of its microstructure, chemical composition, optical properties and photocatalytic activity were conducted. The resulting TiZrNbTaZnO10 exhibited superior UV and visible light absorption, a low bandgap of 2.5 eV, minimal radiative electron–hole recombination and high stability under photocatalytic conditions. Remarkably, TiZrNbTaZnO10 outperformed the TiZrHfNbTaO11 photocatalyst which contains solely d0 electronic configuration. This enhanced performance is attributed to the mixed electronic configurations fostering heterogeneous chemical environments, which facilitate efficient charge carrier separation and transfer.