Iron redox cycling between low-valent oxidation states of Fe^II and Fe^III drives crucial processes in nature. The Fe^II/III redox couple charge compensates the cycling of lithium iron phosphate, a positive electrode (cathode) for lithium-ion batteries. High-valent iron redox couples, involving formal oxidation higher than Fe^III, could deliver higher electrochemical potentials and energy densities. However, because of the instability of high-valent Fe electrodes, they have proven difficult to probe and exploit in intercalation systems. Here we report and characterize a formal Fe^III/V redox couple by revisiting the charge compensation mechanism of (de)lithiation in Li₄FeSbO₆. Valence-sensitive experimental and computational core-level spectroscopy reveal a direct transition from Fe^III (3d⁵) to a negative-charge-transfer FeV (3d⁵L²) ground state on delithiation, without forming Fe^IV, or oxygen dimers. We identify that the cation ordering in Li₄FeSbO₆ drives a templated phase transition to stabilize the unique Fe^V species and demonstrate that disrupting cation ordering suppresses the Fe^III/V redox couple. Exhibiting resistance to calendar aging, high operating potential and low voltage hysteresis, the Fe^III/V redox couple in Li4FeSbO6 provides a framework for developing sustainable, Fe-based intercalation cathodes for high-voltage applications.