In the title salt, [Fe(C12H8N2)3][Fe2Cl6O], the ionic components are linked into a two-dimensional supramolecular layer by two pairs of C—H⋯Cl hydrogen bonds and π–π stacking interactions [centroid–centroid distances = 3.655 (4) and 3.498 (3) Å]. The salt is characterized as a mixed-valent FeII–FeIII compound, in which an FeII atom is coordinated by three phen ligands, forming a six-coordinated cationic entity and the anionic part is formed by two FeIII atoms in tetrahedral coordination environments constructed by three chloride ions and one bridging oxide ligand. Intramolecular C—H⋯N hydrogen bonds are observed.