The quaternary oxide CsTaWO6 exhibits a very high activity for photocatalytic hydrogen generation and water splitting. To improve its properties with regard to photocatalytic applications, it is prepared with mesoporous morphology for the first time, utilizing a template‐based evaporation‐induced self‐assembly process. The resulting material exhibits a median mesopore size of 10 nm, a surface area of 60 m2 g−1, and high crystallinity after preparation at 550 °C with phase‐pure defect‐pyrochlore structure. To further improve the textural properties of mesoporous CsTaWO6, the addition of additives to the synthesis procedure is also investigated. By using H2SO4/HCl and a carbonization/oxidation procedure, the surface area of the resulting mesoporous CsTaWO6 is increased to 78 m2 g−1, which is a 20‐fold increase compared to a nonporous reference via sol‐gel preparation, also leading to improved photocatalytic activity. By investigating the ability for photocatalytic hydrogen generation, the importance of high surface area and pore diameter of the resulting materials in comparison to nonporous materials is presented. Interestingly, the photocatalytic activity does not increase linearly with surface area, due to a strong influence of the pore diameter on the photocatalytic activity.