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In this work, we have explored for the first time the potential application of trace‐Fe(III)/chlorine system as an innovative oxidation technology for the degradation of persistent textile dyes. Fe(III)/chlorine combination improved the dye removal by ~40% within 30 s, as compared with chlorination alone, mainly through a radical pathway induced by the catalytic activation of chlorine in the presence of Fe(III). A chemical probe method was used for identifying the main reactive species. Cl2●− was found to be the key species responsible of huge abatement of dyes in the Fe(III)/chlorine system, whereas ●OH and Cl● can participate with only ~5% in the overall removal efficiency. At pH 3, 77% of reactive green 12 (RG12) was removed after 30 s, and then the removal efficiency diminished to 60% at pH 4, 20% at pH 5, and ~10% at pH 6 and 7. However, the best implication of free radicals was achieved at pH 4, at which the degradation rate was 3.3 time higher than that of chlorination alone. The dye removal efficiency increased with an increase in chlorine and iron loads up to certain optimums, but detrimental effect was observed at higher dosage levels. An increase in the solution temperature notably accelerated the removal yield (i.e., 81% of RG12 was removed at 50°C against 67% at 30°C and 57% at 10°C). NO2− and HSO3− as well as the cationic surfactant Adogen 464 showed strongest inhibiting effect on the performance of the process. Based on these findings, the Fe(III)/chlorine process is highly efficient in removing dyes from wastewaters.