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The direct coupling of methane from natural gas and shale gas is an essential chemical process to produce C2 products which are substrates for polymers, resins, and various functional organic compounds. An appropriate catalyst is necessary to achieve high selectivity to convert methane to the target products. In this study, we investigated the ability of in situ-generated bimetallic Ru–Sn particles to catalyze the non-oxidative coupling of methane to C2 species at 500 °C and observed C2 products’ selectivity of >99% in hydrocarbons. The addition of Sn to Ru resulted in the suppression of coke formation while maintaining the conversion rate of methane to hydrocarbons. X-ray absorption fine structure analysis revealed the mechanism of the in situ formation of Ru–Sn bimetallic particles on the surface of the support. Ru(IV) is initially reduced to Ru(0) particles under methane flow at 400–500 °C. Then, Sn(IV) species around the Ru particles are reduced and dispersed on the outer surface of the Ru particles at 500 °C, although the Sn species were not reduced without Ru at 500 °C. These results point out that Sn(IV) is reduced by active hydrogen atoms generated by the reaction between Ru particles and methane molecules. Hydrogen spills over the surface and reduces the Sn(IV) species. This in situ-formed Ru–Sn bimetallic species showed good performance for non-oxidative coupling of methane.