Guanidinium hydrogen glutarate (GHG) was synthesized by slow evaporation method. X-ray diffraction (XRD) study reveals that GHG crystallized into a triclinic system with the space group P$\bar{1}$. Crystallinity of the obtained GHG crystal was investigated with the help of the powder XRD analysis. High-intensity peak observed at 28° of the (1 –1 –2) plane confirms the good crystallinity of the GHG crystal. The crystalline nature of the synthesized crystal was tested through high-resolution XRD. The presence of different functional groups in the GHG material was analysed by the Fourier transform infrared and FT-Raman spectra. UV–Vis spectral analysis of the GHG material demonstrates 98% transmittance with a cut-off wavelength at 230 nm. The bandgap value of GHG is 5.01 eV. A peak at 421 nm is observed in the emission spectrum. The results imply that GHG crystals have a blue fluorescence emission. The thermal stability of the grown crystal was determined using thermal analysis. The GHG compound is stable up to 244°C and it has good degree of crystallinity. The mechanical behaviour of the title crystal was measured using microhardness studies. The GHG crystal shows that it belongs to soft material category. A dielectric study of the crystal was analysed at diverse temperatures. Third-order nonlinear optical (NLO) susceptibility is determined using through Z-scan studies. The nonlinear refractive index ($n_2$), nonlinear absorption coefficient (${\beta}$) and third-order NLO susceptibility (${\chi}^(3)$) were estimated to be –1.8545 ${\times}$ 10$^{–8}$ (cm$^2$ W$^{–1}$), 3.8015 ${\times}$ 10$^{–4}$ (cm W$^{–1}$) and 2.2150 ${\times}$ 10$^{–5}$ (esu), respectively. Optical limiting property of the GHG compound has also been discussed.