Oxygen reduction reaction (ORR) is a complex 4e–/4H+ multistep process, and factors that determine the rate and selectivity of this reaction are a matter of contemporary interest. Synthetic iron porphyrin model complexes mimicking the active site of horseradish peroxidase (HRP) are shown to enhance the rate of ORR and 4H+/4e– selectivity irrespective of the rate of electron transfer from the electrode relative to unfunctionalized iron porphyrins. In operando spectroscopic analysis over self-assembled monolayer-modified electrodes allows characterization of reactive intermediates involved in ORR. Two key intermediate species of ORR, FeIII–OOH and FeIVO, are identified using 18O2 labeling depending on the nature of the pendant residue of these HRP mimics. The results indicate that the nature of the pendant distal moiety in the distal superstructure of iron porphyrin changes the distribution of the intermediate species under steady state relative to simple mononuclear porphyrins. Density functional theory calculations indicate that not only the presence of hydrogen bonding from the pendant groups but also its relative spatial orientation with respect to the proximal and distal oxygen atom of a FeIII–OOH intermediate species controls the selectivity of ORR.