The rational design of catalytically active sites in porous materials is essential in electrocatalysis. Herein, atomically dispersed Fe‐Nx sites supported by hierarchically porous carbon membranes are designed to electrocatalyze the hydrazine oxidation reaction (HzOR), one of the key techniques in electrochemical nitrogen transformation. The high intrinsic catalytic activity of the Fe‐Nx single‐atom catalyst together with the uniquely mixed micro‐/macroporous membrane support positions such an electrode among the best‐known heteroatom‐based carbon anodes for hydrazine fuel cells. Combined with advanced characterization techniques, electrochemical probe experiments, and density functional theory calculation, the pyrrole‐type FeN4 structure is identified as the real catalytic site in HzOR. Hierarchically porous carbon membrane‐supported atomically dispersed pyrrole‐type FeN4 sites are proposed and verified as real active sites for the hydrazine oxidation reaction.