The title compound, C13H10N+·C7H4NO4 , consists of a protonated acridinium cation and a 6-carboxypyridine-2-carboxylate monoanion. The carboxylate group of the anion appears to be delocalized on the basis of the nearly equivalent C—O bond lengths. In the crystal, the anions are connected by strong O—H...O hydrogen bonds, forming chains along the b axis. The acridinium cations are linked to the anionic chains by strong N—H...O hydrogen bonds between the carboxylate group of the anion and the N—H group of the cation. Along the b axis, successive chains stack in opposite directions. Weak intermolecular C—H...O hydrogen bonds further stabilize the crystal structure.