The asymmetric unit of the title co-crystal, 2C14H13N2+·C10H4O82−·2C14H12N2·C10H6O8, comprises a 2,9-dimethyl-1,10-phenanthrolin-1-ium cation (Me2PhenH+) and a 2,9-dimethyl-1,10-phenanthroline molecule (Me2Phen), each in a general position, and half each of a 2,5-dicarboxybenzene-1,4-dicarboxylate dianion (LH22−) and a benzene-1,2,4,5-tetracarboxylic acid molecule (LH4), each being disposed about a centre of inversion. Small twists are evident in the dianion [the C—C—C—O torsion angles are 168.41 (18) and 16.2 (3)°], whereas a major twist is found for one carboxylic acid group in the neutral molecule [C—C—C—O = 66.3 (2) and 18.2 (3)°]. The most prominent feature of the crystal packing is the formation of linear supramolecular chains along  mediated by charge-assisted O—H⋯O− hydrogen bonding between alternating LH4 and LH22−. These are connected to the Me2PhenH+ and Me2Phen species by N—H⋯O and O—H⋯N hydrogen bonds, respectively. A three-dimensional architecture is formed by C—H⋯O and π–π interactions [inter-centroid distance = 3.5337 (17) Å].