Guanidinium fumarate dihydrate (GFDH), an organic material was grown by slow evaporation method at room temperature. The monoclinic system of the GFDH crystal was affirmed by single XRD analysis and its space group was determined to be P2₁/n. The quality of the grown optical GFDH crystal was confirmed with HRXRD analysis. The molecular structure of the GFDH crystal was studied by FT-IR spectroscopy. UV–Vis study demonstrates the lower cut-off wavelength (320 nm) and higher optical transparency of the GFDH crystal. The Meyer’s index value (n = 1.23) of the GFDH crystal shows that the GFDH crystal belongs to hard material category. Information regarding the thermal stability and melting point were rendered from the TG–DTA thermal studies. Dielectric studies were performed to understand the various polarization mechanisms at different temperatures. The GFDH crystal exhibits high third-order non-linear optical properties and optical limiting properties and that was analyzed by the Z-scan technique.