In this work, morphology-controlled SrTiO3/Ti film catalysts were constructed on Ti foil via a two-step hydrothermal strategy, followed by the introduction of highly dispersed Rh species to regulate the photocatalytic CO2 reduction behavior. By tuning the hydrothermal parameters, controllable evolution among nanowire, nanosheet, and nanoparticle architectures was achieved. The results demonstrate that moderately suppressing the dissolution–reprecipitation process favors the formation of nanosheet structures with higher specific surface area and enriched oxygen vacancies, thereby significantly enhancing light absorption and charge carrier separation efficiency. On this basis, the 0.04Rh/SrTiO3 sample with an actual Rh loading of 0.0941 wt% exhibited the optimal performance, delivering a CH4 production rate of 35.62 µmol g−1 h−1 with 100% selectivity toward gaseous carbon-containing products. CO-DRIFTS and aberration-corrected STEM analyses confirm that Rh exists in the form of highly dispersed single atoms and clusters. In situ FT-IR results reveal that the synergistic interaction between Rh sites and oxygen vacancies promotes the sequential hydrogenation of CO2 toward *COOH and *CHx intermediates while suppressing *CO desorption, thereby steering the reaction along a deep-reduction pathway toward CH4 formation. This study provides new structural insights and mechanistic understanding for constructing highly selective photocatalytic systems for CO2-to-CH4 conversion.