Single Mn atom on nitrogen‐doped graphene (MnN4‐G) has exhibited good structural stability and high activity for the adsorption and dissociation of an O2 molecule, becoming a promising single‐atom catalyst (SAC) candidate for oxygen reduction reaction (ORR). However, the catalytic activity of MnN4‐G for the ORR and the optimal reaction pathway remain obscure. In this work, density‐functional theory calculations were employed to comprehensively investigate all the possible pathways and intermediate reactions of the ORR on MnN4‐G. The feasible active sites and the most stable adsorption configurations of the intermediates and transition states during the ORR were identified. Screened from all the possibilities, three optimal four‐electron O2 hydrogenation pathways with an ultralow energy barrier of 0.13 eV were discovered that are energetically more favorable than direct O2 dissociation pathways. Analysis of the free energy diagram further verified the thermodynamical feasibility of the three pathways. Thus, MnN4‐G possesses superior ORR activity. This study provides a fundamental understanding of the design of highly efficient SACs for the ORR. Taking the indirect route: All the possible reaction pathways for oxygen reduction on single Mn atom anchored on nitrogen‐doped graphene including intermediates, H+ adsorption sites, and transition states have been investigated by DFT calculations. Four‐electron O2 hydrogenation pathways were found to be energetically more favorable than direct O2 dissociation pathways, with energy barriers as low as 0.13 eV.