State-of-the-art processes to directly convert methane into CH3Cl are run under corrosive conditions and typically yield a mixture of chloromethanes requiring subsequent separation. We report a mechanochemical strategy to selectively convert methane to chloromethane under overall benign conditions, employing trichloroisocyanuric acid (TCCA) as a cheap and noncorrosive solid chlorinating agent. TCCA is shown to release active chlorine species upon milling with Lewis acids such as alumina and ceria to functionalize methane at moderate temperatures (<150 °C). A thorough parameter optimization led to a maximum methane chlorination rate of 0.8 μmol(CH4,conv) (g(catalyst) s)-1. Findings were compared to the thermal reaction of methane with TCCA and evidenced that mechanochemical activation permitted significantly lower reaction temperatures (90 vs 200 °C) at a drastically improved CH3Cl selectivity (95% vs 66% at 30% conversion). Considering the characterization of the interaction between TCCA and Lewis acids as well as the in-depth analysis of byproducts, we suggest a plausible reaction mechanism and a possible regeneration of the chlorinating agent.