Combining the advantages of homogeneous and heterogeneous catalysts, single‐atom catalysts (SACs) are bringing new opportunities to revolutionize ORR catalysis in terms of cost, activity and durability. However, the lack of high‐performance SACs as well as the fundamental understanding of their unique catalytic mechanisms call for serious advances in this field. Herein, for the first time, we develop an Ir‐N‐C single‐atom catalyst (Ir‐SAC) which mimics homogeneous iridium porphyrins for high‐efficiency ORR catalysis. In accordance with theoretical predictions, the as‐developed Ir‐SAC exhibits orders of magnitude higher ORR activity than iridium nanoparticles with a record‐high turnover frequency (TOF) of 24.3 e− site−1 s−1 at 0.85 V vs. RHE) and an impressive mass activity of 12.2 A mg−1Ir, which far outperforms the previously reported SACs and commercial Pt/C. Atomic structural characterizations and density functional theory calculations reveal that the high activity of Ir‐SAC is attributed to the moderate adsorption energy of reaction intermediates on the mononuclear iridium ion coordinated with four nitrogen atom sites. Ir‐N‐C: Single‐atom catalysts (SACs) combine the advantages of homogeneous and heterogeneous catalysts. A single‐atom iridium catalyst coordinated with four nitrogen atoms has been designed and synthesized to mimic homogeneous iridium porphyrins for high‐efficiency oxygen reduction reaction catalysis.