Efficient degradation of per- and polyfluoroalkyl substances (PFAS) remains a significant challenge due to its recalcitrant nature. In this study, a bismuth (Bi)/titanium (Ti) bimetallic coordination photocatalyst, featuring metal cation centers bridged by ligands, was synthesized. The incorporation of Bi and Ti resulted in coordinatively unsaturated metal sites that facilitate strong interactions with perfluorooctanoic acid (PFOA) via Ti−O and Bi−F complexation. The resulting electron redistribution towards the C−F bonds of PFOA facilitated bond weakening, thereby enabling the bimetallic coordination photocatalyst to effectively activate PFOA for degradation under UV₂₅₄ irradiation. Even an ultralow dosage (5 mg L⁻¹) resulted in complete PFOA degradation and 56.8 % defluorination within 5 h. Analysis of PFOA degradation intermediates identified short chain perfluorocarboxylic acids as the primary products. This study explores an ultralow-dosage, high-efficiency photocatalytic strategy based on Ti/Bi bimetallic coordination polymers, enabling effective PFOA degradation and defluorination by exploiting unsaturated metal sites on the catalyst surface. In addition to its practical implications for water purification, this approach elucidates the mechanistic insights into C−F bond activation and underscores a generalizable design strategy for developing catalysts targeting persistent organic pollutants.