A single crystal of 4-dimethylaminopyridinium p-hydroxybenzoate pentahydrate (DMAPHB) was obtained via a slow evaporation solution growth technique. Single crystal X-ray diffraction studies of the as-grown crystal show that the crystal belongs to a monoclinic system with P2₁/c space group. The asymmetric part of the title compound contains three DMAPHB molecules and five water molecules. Interplay between a vast number of intermolecular interactions such as strong O–H⋯O, N–H⋯O and weak C–H⋯O hydrogen bonds are discussed. Spectroscopic studies such as FT-IR, FT-Raman, NMR and UV-Vis were carried out to reveal the molecular properties and optical behaviour. The mechanical strength of DMAPHB was examined using Vickers microhardness test. The thermal stability and melting point of the crystal were studied by TG-DTA analysis. The third order non-linear optical behaviour of the title compound was studied using the Z-scan technique. Antibacterial biological evaluation of the material was carried out using a resazurin reduction assay method against Escherichia coli, Staphylococcus aureus and Bacillus cereus.