In nature, plants convert solar energy into chemical energy via water oxidation. Inspired by natural photosynthesis, artificial photosynthesis has been gaining increasing interest in the field of sustainability/green science and technology as a non-natural and thermodynamically endergonic (ΔG° > 0, uphill) solar-energy-driven reaction that uses water as an electron donor and a source material. Among the artificial-photosynthesis processes, inorganic-synthesis reactions via water oxidation, including water splitting and CO2-to-fuel conversion, have been attracting much attention. In contrast, the synthesis of high-value functionalized organic compounds via artificial photosynthesis, which we have termed artificial photosynthesis directed toward organic synthesis (APOS), remains a great challenge. Herein, we report a synthetically pioneering and meaningful strategy of APOS, where the carbohydroxylation of C = C double bonds is accomplished via a three-component coupling with H2 evolution using dual functions of semiconductor photocatalysts, i.e., silver-loaded titanium dioxide (Ag/TiO2) and rhodium–chromium–cobalt-loaded aluminum-doped strontium titanate (RhCrCo/SrTiO3:Al). Emulating the concept of natural photosynthesis has long been a focus of chemists in an effort to harness solar light as an energy source using water as an electron donor and a source material. Here, the authors present an artificial photosynthetic system that can functionalize styrenes via C–H activation and water splitting.