Optically good quality organic single crystals of imidazolium 3-nitrobenzoate (I3NB) have been grown by slow evaporation solution technique (SEST). The I3NB crystallized in monoclinic crystal system with space group P21/c, which is concluded from single crystal XRD analysis and the PXRD pattern was obtained for the crystal. The I3NB crystal was subjected to FTIR and FT-Raman spectral analyses to identify the functional groups of the I3NB compound. The optical transparency of the crystal was 80% and the cut-off wavelength was observed to be 321 nm. Thermal stability of the material was studied by TG/DTG and DSC analysis. The mechanical properties (hardness, yield strength and stiffness constant) of the crystal were analyzed by Vickers microhardness test. The electrical conductivity of the crystal was carried out by dielectric study. Z-scan method was adopted to investigate the third order nonlinear optical (NLO) properties of the crystal. Additional insight was gained from the theoretical investigation for the I3NB crystal. To achieve that, Density Functional Theory (DFT) calculations have been performed under solvation model to understand the geometrical and electronic structural features like frontier molecular orbital analysis (FMO), natural bond orbital analysis (NBO), molecular electrostatic potential (MEP) studies, dipole moment, polarizability and hyperpolarizability of the crystal. All these findings approve that the I3NB crystal is favorably suitable for NLO applications. © 2019