Simultaneous photocatalytic reactions of H₂ evolution and real wastewater degradation have attracted much attention for practical energy and environmental applications. However, the photocatalysts employed for these applications often suffer from high charge-carrier recombination and poor efficiency in activating the reactants, resulting in unsatisfactory photocatalytic activity or the need for an expensive platinum co-catalyst. Herein, an unsaturated iron ion-based coordination polymer (FeTMT) with weak Fe–N sites was fabricated via a facile wet-chemical method. It exhibited an outstanding photocatalytic performance for the simultaneous production of H₂ (1272 μmol g⁻¹ h⁻¹) and degradation of real wastewater from brewing liquor (degradation efficiency of 60%) without the use of any cocatalyst, which is higher than that of the reported systems. Density functional theory (DFT) calculations revealed that the unsaturated Fe–N bridges can transfer electrons from the C₃N₃S₃ rings to Fe³⁺, boosting the separation and transportation efficiency of charge carriers. Alternatively, the N functional group close to the metal centers in FeTMT can be regarded as a proton relay to enhance the surface hydrophilicity. Further, the in situ test demonstrated that the unsaturated Fe sites can adsorb H⁺ to form an H–Fe–H bond, while the Fe–N sites serve as the catalytic active centers in FeTMT. This finding opens an avenue to construct novel coordination polymers and gain deep understanding for the practical industrial application of photocatalysis.