AbstractDeveloping sustainable cost‐effective strategies for valorization of field‐spent granular activated carbon (s‐GAC) from industrial water treatment has gained much interest. Here, we report a cost‐effective strategy for the regeneration of s‐GAC as an adsorbent in a large‐scale drinking water treatment plant and used as an efficient and durable ozonation catalyst in water. To achieve this, a series of samples is prepared by subjecting s‐GAC to thermally controlled combustion treatments with and without pyrolysis. The catalytic performance of the optimized sample is evaluated for oxalic acid degradation as the model pollutant under batch (>15 h) and continuous flow operations (>200 h). The partially deactivated catalyst upon reuse is restored by thermal treatment. Electron paramagnetic resonance and selective quenching experiments show the formation of singlet oxygen (1O2) during catalytic ozonation. The GAC‐ozonation catalyst is efficient to minimize the formation of chlorinated disinfection by‐products like trihalomethanes and haloacetic acids in an urban wastewater effluent.