Electrocatalytic advanced oxidation processes have long been considered among of the most viable ways to remediate aquatic contaminants, including As(III). Although direct electrochemical oxidation of As(III) is thermochemically facile, a high reaction rate is not easily achieved because of the competitive oxygen evolution reaction (OER), particularly at high potentials. This study examines the effect of three halides (Cl-, Br-, and I-) on the electrochemical oxidation of As(III) with nanoparticulate TiO2 electrodes in an aqueous bicarbonate solution at pH 8.7. The halides significantly enhance As(III) oxidation kinetics by >4, >8, and >20 times, respectively, under optimal conditions. Faradaic efficiencies of As(V) production (AsV-FEs) are also enhanced by a maximum of 10 times by the halides, even at high potentials at which the OER occurs. Pre-electrolysis of each halide solution produces reactive halogen species (ClO-, BrO-, and I3-). As(III)-spiking of the pre-electrolyzed halide solutions allows simultaneous concentration changes at near-stoichiometric ratios (R2 > 0.98) between each halogen species and As(V). Among the three halides, iodide imparts the strongest effect on As(III) oxidation owing to its lowest redox potential. Finally, technical considerations of reactive-halogen-species-mediated As(III) oxidation are discussed.