In the work, S-doped iron-based carbon nanocomposites (Fe–S@CN) for activating persulfate (PS) were prepared by calcining iron-loaded sodium lignosulfonate. The characterization revealed that the main substances of Fe–S@CN were FeS and Fe3C, which were distributed on porous carbon nanosheets in rod-like morphology. In the Fe–S@CN/PS system, carbamazepine could be completely removed within 30 min, and the relative contribution of hydroxyl radicals (OH·), sulfate radicals (SO4·-) and total singlet oxygen (1O2) and superoxide radicals (O2·-) for carbamazepine removal were approximated as 8.7%, 19.2% and 72.1%, respectively. Electron paramagnetic resonance spectroscopy demonstrated that S doping promoted the formation of various active species. Compared with the catalyst without S doping, Fe–S@CN exhibited higher activation performance (1.48-fold) for PS due to the enhanced electron transfer rate and facilitated Fe2+/Fe3+ cycle. Density functional theory calculations showed that S doping promoted the binding between the catalyst and PS, and enhanced the overall internal electron density of the catalyst. Fe–S@CN exhibited excellent catalytic performance over a wide pH range (3.0–11.0). The active sites of Fe–S@CN used in the cycling experiments was also largely recovered after thermal regeneration. Overall, this study shows for the first time the impact of SLS as an S dopant on enhanced PS activation.