Effective integration of hierarchically porous architecture and high-density distribution of dopant sites into carbon is essential to improve the activity of heteroatom-doped carbon for oxygen reduction reaction (ORR). Herein, we present a general sealed space-assisted approach to fabricate N,P-codoped porous carbon networks (NP-PCN) by calcination of a self-assembled mixture of C₆H₁₄N₂O₂, NH₄H₂PO₄, and NaCl. The NaCl assemblies serve as a space-enclosed nanoreactor for the effective formation of hierarchical pores with high surface area and dense N,P-induced dopants by preventing the loss of N,P-containing gasses from the decomposition of precursors during annealing. The NP-PCN is applied as an ORR catalyst and exhibits excellent performance with a positive half-wave potential of 0.82 V vs. RHE, a low Tafel slope of 59 mV dec⁻¹, high tolerance to methanol, and high durability in alkaline media, making NP-PCN a promising alternative to costly platinum for the ORR. The enhanced performance is attributed to the combination of hierarchical pores and optimized N,P codoping, which significantly enhances the available number of catalytic sites by exposing the N,P-induced dopants and facilitates mass transfer in the ORR process. This finding opens a new avenue for the design of advanced porous carbons to improve their electrocatalytic activity.