In the current research, (E)-4-(3-hydroxy-4-methoxystyryl)-1-methyl pyridinium iodide monohydrate (HMSI) has been prepared through Knoevenagel condensation and crystallized by slow evaporation technique. Crystallographic analysis has been carried out to study the crystal structure and unit cell parameters. The fundamental vibration frequencies of specific chemical functional groups were detected by infrared absorption spectrum. Further the molecular structure of the grown crystal was confirmed by nuclear magnetic resonance spectroscopic analysis. Thermal stability (145 °C) and meting point (248 °C) of the HMSI material have been elaborated by means of thermogravimetric and differential scanning calorimetric (TG/DSC) analysis. The crystal was found to be transparent above 460 nm with the band gap of 2.63 eV obtained from transmission spectral analysis. The growth features of HMSI crystal were examined to check for the defects using an optical microscope. Crystal surface damage by Nd: YAG laser at 1.064 μm radiation was measured to be 1.98 GW/cm2. Further, the nonlinear response of HMSI has been studied using Z-scan technique and it was found that the title crystal is capable of exhibiting self-focusing nature with reverse saturable absorption. The evaluated nonlinear susceptibility is in the order of 10−6 esu which is slightly higher compared to other third-order stilbazolium derivative crystals. © 2018