In this study, nonlinear optical crystalline materials L-histidine hydrochloride monohydrate (LHHCL) and L-histidine methyl ester dihydrochloride (LHMDHCL) were successfully grown by the slow solvent evaporation technique. As-grown crystalline materials were subjected to X-ray structure analysis, FT Raman spectroscopy, energy-dispersive X-ray spectroscopy, UV–Vis spectroscopy, frequency conversion analysis, dielectric, and Vicker’s microhardness studies. According to XRD data, the grown crystal LHHCL was crystallized to an orthorhombic form having a space group P212121, while the LHMDHCL crystal belongs to a monoclinic form with a space group P21. The FT-Raman study confirms the existence of chemical groups and the formation of two different crystals. The chemical compositions of the as-grown crystalline materials were established by Energy-dispersive X-ray spectroscopy. The UV–Vis study substantiates the transparency of LHHCL and LHMDHCL in the wavelength regions of 232–1000 nm and 230–1000 nm, respectively. Using the Tauc equation, the bandgap energy was determined as 5.35 eV and 5.38 eV for LHHCL and LHMDHCL crystals, respectively. In addition, the grown crystals have shown a better frequency conversion efficiency in comparison to KDP samples. According to the dielectric study, dielectric characteristics such as dielectric constant and dielectric loss for the LHHCL and LHMDHCL crystals drop as frequency increases. The hardness of the LHHCL and LHMDHCL crystals was measured by the Vickers microhardness test which reveals that the grown crystals follow the normal indentation size effect.