In the present investigation, two organic nonlinear optical crystals, 2l-histidinium·2maleate·3H2O (2LHM3H) and l-histidinium·glutarate·H2O (LHGH), were produced by the slow solvent evaporation technique. Analytical studies, such as x-ray diffraction (XRD) analysis, Fourier transform Raman (FT-Raman) spectroscopy, Fourier transform nuclear magnetic resonance (FT-NMR) spectroscopy, ultraviolet–visible (UV–Vis) spectroscopy, frequency doubling, and thermal and dielectric tests, were performed on as-grown 2LHM3H and LHGH crystals. According to XRD measurements, 2LHM3H solidified in a monoclinic space group P21, whereas LHGH solidified in an orthorhombic space group P212121. The availability of functional groups and the growth of 2LHM3H and LHGH crystals were revealed by FT-Raman spectroscopy. FT-NMR spectroscopy has been used to establish the molecular structures of as-grown crystals. The transparency of 2LHM3H and LHGH crystals in the wavelength ranges of 280–800 nm and 235–800 nm, respectively, was identified by the UV–Vis measurements. The bandgap energies of 2LHM3H and LHGH crystals were calculated using the optical transmittance spectra, and the values were found to be 4.45 eV and 5.25 eV, respectively. Second harmonic generation (SHG) testing was used to examine the frequency conversion efficiency of the obtained crystals. The phase transition and thermal degradation of the crystallized substances have been investigated using thermogravimetry/derivative thermogravimetry (TG/DTG) studies. The dielectric properties of 2LHM3H and LHGH crystals were ascertained using dielectric tests.