A non-thermal plasma with a wet scrubber (NTP + WS) was used to degrade gaseous toluene. Compared with the NTP + WS/H2O system, the toluene and by-product ozone removal efficiencies were increased by 10% and 85% in the NTP + WS/Fe2+ system, respectively. For 60 ppm toluene degradation, the maximum mineralization rate (MR) of toluene (61%) was obtained, at the optimum Fe2+ concentration of 50 mg/L. During catalytic oxidation, the removal efficiency of toluene was limited by its solubility in WS systems. In addition, decreased Fe2+ concentration and accumulation of organics led to the system deactivation. The EPR and quenching experiments verified the presence and contribution of hydroxyl radicals (4.6%) and superoxide radicals (3.8%) to the removal efficiency of toluene. Based on the radicals and intermediates detected in the gas and liquid phases, a degradation mechanism for toluene in the NTP + WS/Fe2+ system was proposed.