The slow evaporation solution growth technique was used to successfully grow N -allylthiourea (NAT) crystals. The grown crystal was confirmed to be centrosymmetric space group P2 1 /c with monoclinic system using single-crystal X-ray diffraction analysis. Fourier transforms infrared and Raman analysis established the functional group of the grown crystal. Furthermore, the thermal stability of the compound was determined using thermogravimetric and differential thermal analysis. A spectroscopic analysis of UV–Vis-NIR transmission reveals a lower cutoff wavelength of 260 nm and an energy gap of 3.9 eV. The photoluminescence analysis shows the emission of the grown crystal at 336 nm in UV region. Third-order nonlinear optical parameters such as nonlinear refractive index ( n 2  = 2.88 × 10 –7  cm 2 /W), nonlinear absorption coefficient ( β  = 9.05 × 10 –3  cm/W) and third-order nonlinear susceptibility ( χ 3  = 3.27 × 10 −5  esu) have been calculated using Z scan studies. In addition, computational studies including molecular geometry optimization, Mulliken atomic charge analysis and HOMO–LUMO analysis have been conducted by means of B3LYP method at 6-311+G(d,p) to explore different intermolecular interactions. Further, the molecular electrostatic potential is used to visualize and predict potential nucleophilic and electrophilic interactions.