AbstractNitrogen (N) doping of graphene with a three‐dimensional (3D) porous structure, high flexibility, and low cost exhibits potential for developing metal–air batteries to power electric/electronic devices. The optimization of N‐doping into graphene and the design of interconnected and monolithic graphene‐based 3D porous structures are crucial for mass/ion diffusion and the final oxygen reduction reaction (ORR)/battery performance. Aqueous‐type and all‐solid‐state primary Mg–air batteries using N‐doped nanoporous graphene as air cathodes are assembled. N‐doped nanoporous graphene with 50–150 nm pores and ≈99% porosity is found to exhibit a Pt‐comparable ORR performance, along with satisfactory durability in both neutral and alkaline media. Remarkably, the all‐solid‐state battery exhibits a peak power density of 72.1 mW cm⁻²; this value is higher than that of a battery using Pt/carbon cathodes (54.3 mW cm⁻²) owing to the enhanced catalytic activity induced by N‐doping and rapid air breathing in the 3D porous structure. Additionally, the all‐solid‐state battery demonstrates better performances than the aqueous‐type battery owing to slow corrosion of the Mg anode by solid electrolytes. This study sheds light on the design of free‐standing and catalytically active 3D nanoporous graphene that enhances the performance of both Mg–air batteries and various carbon‐neutral‐technologies using neutral electrolytes.