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Currently, single‐atom catalysts (SACs) research mainly focuses on transition metal atoms as active centers. Due to their delocalized s/p‐bands, the s‐block main group metal elements are typically regarded as catalytically inert. Herein, an s‐block potassium SAC (K−N−C) with K‐N4 configuration is reported for the first time, which exhibits excellent oxygen reduction reaction (ORR) activity and stability under alkaline conditions. Specifically, the half‐wave potential (E1/2) is up to 0.908 V, and negligible changes in E1/2 are observed after 10,000 cycles. In addition, the K−N−C offers an exceptional power density of 158.1 mW cm−2 and remarkable durability up to 420 h in a Zn‐air battery. Density functional theory (DFT) simulations show that K−N−C has bifunctional active K and C sites, can optimize the free energy of ORR reaction intermediates, and adjust the rate‐determining steps. The crystal orbital Hamilton population (COHP) results showed that the s orbitals of K played a major role in the adsorption of intermediates, which was different from the d orbitals in transition metals. This work significantly guides the rational design and catalytic mechanism research of s‐block SACs with high ORR activity. [ABSTRACT FROM AUTHOR]