Lithium–sulfur (Li–S) batteries demonstrate remarkable theoretical capacity and energy density; however, the practical application is hindered by large Li$^+$ desolvation barriers and polysulfide shuttling, exhibiting the cascade sulfur reactions. Herein, single atomic cobalt atoms are anchored onto nitrogen-doped polymeric carbon spheres (SACo@NPCS) via polymerization and pyrolysis, serving as the cascade catalyst to promote reaction kinetics in harsh conditions. Specifically, cobalt single atoms with high electronegativity and catalytic efficiency enhance the interactions with sulfur species and reduce the energy barrier of deposition and decomposition of Li2S after accelerating the desolvation and diffusion of Li(solvent)$_x$$^+$ in advance, as comprehensively verified through theoretical simulations and experimental electrochemical tests. Impressively, the optimal cell maintains stable operation for over 300 cycles under a sulfur loading of 5.4 mg cm$^{–2}$ and tolerates the high-rate capability up to 5 C even at 0 °C, highlighting the promise of atom-level cascade catalysts for practical implementation.