Carbon-based single-atom iron electrocatalysts with nitrogen coordination (CSAIN) have recently shown enormous promise to replace the costly Pt for boosting the cathodic oxygen reduction reaction (ORR) in fuel cells. However, there remains a great challenge to achieve highly efficient CSAIN catalysts for the ORR in acidic electrolytes. Herein, a novel CSAIN catalyst is synthesized by pyrolyzing a precursor mixture consisting of metal–organic framework and conductive polymer hybrid. After pyrolysis at a high temperature, the CSAIN with a structure of carbon nanosheet supported polyhedral carbon is achieved, where the unique structure endows CSAIN with expediting electron transfer and mass transport, as well as largely exposed surface to host atomically dispersed iron active sites. As a result, the optimal CSAIN catalyst shows a high ORR activity with its half-wave potential of 0.77 V (vs RHE) and a Tafel slope of 74.1 mV dec–1, which are comparable to that of commercial Pt/C catalyst (0.80 V and 81.9 mV dec–1).