In the complex cation of the title compound, [Zn(C17H13N2O2)2(H2O)4](C10H4O8)2·2.5H2O, the ZnII atom, lying on an inversion center, is coordinated by two N atoms from two N-(3-carboxyphenyl)-4,4′-bipyridin-1-ium ligands and four water molecules in a distorted octahedral geometry. The pyromellitate anion is double deprotonated. O—H...O and C—H...O hydrogen bonds connect the cations, anions and uncoordinated water molecules into a three-dimensional supramolecular network. One of the two lattice water molecules shows an occupancy of 0.25. An intramolecular O—H...O hydrogen bond is present in the anion.