In summary, we have demonstrated unprecedented hemoprotein-catalyzed [1,2]-Stevens rearrangement in the context of a one-carbon ring expansion of aziridines to azetidines. This system not only represents a rare example of a highly enantioselective [1,2]-Stevens rearrangement of ammonium ylides, but also exhibits unprecedented selectivity for the [1,2]-Stevens rearrangement of aziridinium ylides over cheletropic extrusion of ethylene. We are optimistic that observed selectivities can be extended to other types of [1,2]-Stevens rearrangements, providing the grounds for future work in this area toward the synthesis of enantioenriched heterocycles and other chiral amines.