In the centrosymmetric dinuclear complex anion of the title compound, (C5H8N3)2[Bi2(C7H3NO4)4(H2O)2]·4H2O, the BiIII atom is eight-coordinated in an N2O6 environment and has a distorted bicapped trigonal–prismatic coordination environment. Extensive inter­molecular O—H⋯O, N—H⋯O and weak C—H⋯O hydrogen bonds lead to the stability of the crystal structure. Inter­actions between one C—H group of the 2,3-diamino­pyridinium [(2,3-dapyH)+] cation and the aromatic ring of the pyridine-2,6-dicarboxyl­ate (pydc) ligand (C—H⋯centroid distance = 2.78 Å) and π–π inter­actions between the (2,3-dapyH)+ cations and between the (2,3-dapyH)+ cation and the pydc ligand [centroid–centroid distances = 3.489 (5) and 3.694 (5) Å] are observed.