Developing highly efficient electrocatalysts is crucially significant for the application of advanced energy conversion. The Fe–N–C single-atom catalyst is promising for CO₂ electroreduction reaction (CO₂RR) but suffers from insufficient intrinsic activity and inferior conductivity, which could be addressed by redistributing the electron density via heteroatom doping. Herein, we synthesized S-doped Fe–N–C (Fe–SN–C) as an advanced electrocatalyst for CO₂RR using a simple trapping–pyrolysis strategy. Density functional theory calculations and experimental results indicate that S doping increases the d-band electrons and conductivity of Fe–SN–C by electron donating, and thus boosts *CO desorption during the CO₂RR process and suppresses the competing hydrogen evolution reaction. Consequently, Fe–SN–C exhibits the maximum CO faradaic efficiency of 93% at −0.5 V and the highest partial current density of 10.1 mA cm⁻² at −0.8 V for 2e⁻ CO₂RR. This finding provides a feasible and controllable method to achieve advanced electrocatalysts for efficient energy conversion.