The asymmetric unit of the title compound, [Mn(C7H4NO4)(2)(C6H6N2O)(2)(H2O)(2)], contains one Mn-II atom, one 4-nitrobenzoate (NB) anion, one nicotinamide (NA) ligand and one water molecule; NA and NB each act as a monodentate ligand. The Mn-II atom, lying on an inversion centre, is coordinated by four O atoms and two pyridine N atoms in a distorted octahedral geometry. The water molecules are hydrogen bonded to the carboxylate O atoms. The dihedral angle between the carboxylate group and the adjacent benzene ring is 24.4 (3)degrees, while the benzene and pyridine rings are oriented at a dihedral angle of 86.63 (11)degrees. In the crystal, O-H center dot center dot center dot O and N-H center dot center dot center dot O hydrogen bonds link the molecules, forming a layer parallel to the ab plane. The layers are further linked via weak C-H center dot center dot center dot O hydrogen bonds, a pi-pi stacking interaction [centroid-centroid distance = 3.868 (2) angstrom] and a weak C-H center dot center dot center dot pi interaction, resulting in a three-dimensional network.