• GPI single crystals were grown by slow evaporation method. • Functional groups of the crystal were identified by FTIR spectral analysis. • The SHG efficiency is 0.89 times that of KDP. • Third-order nonlinear optical susceptibility (χ 3 ) was found to be 3.79 × 10 −6 esu. Using the slow solvent evaporation method with deionized water as the solvent, a single crystal of glycine potassium iodide (GPI) was grown at room temperature. The GPI crystal belongs with space group Cc to the monoclinic system. Functional groups present in the sample were identified by FTIR spectral analysis. The crystals were further characterized by UV-Vis NIR transmission spectrum in the range of 250–1100 nm. Second Harmonic Generation was validated in the Kurtz-Perry powder technique. The Z-scan experiment was being used to assess the nonlinear absorption coefficient, nonlinear refractive index and third-order nonlinear susceptibility to explore GPI crystal third-order NLO behavior. The photoconductivity study confirms the grown crystal is positive photoconductivity. The grown crystal suitability for nonlinear optical applications was confirmed through characterization studies.