Single crystals of 4-acetylanilinium dihydrogen phosphate (4AADP), a novel third-order nonlinear optical material has been synthesized and successfully grown by the slow evaporation solution growth technique using acetone as a solvent at room temperature. The single crystal X-ray diffraction analysis implies that 4AADP crystallized into a monoclinic crystal system with the centrosymmetric space group P2 1 /c. The molecular structure of the grown 4AADP compound was evidently established by using 1 H and 13 C NMR spectral analysis. The vibrational behavior of the chemical bond and discrete functional groups of the grown crystal were identified using FT-IR and FT-Raman spectral analysis. UV–Visible-Near Infrared spectral analysis shows that the grown crystal was highly transparent in the entire visible range above 365 nm. The 4AADP compound was thermally stable up to 195 °C and it was ascertained by thermogravimetric and differential scanning calorimetric analysis. The photoactive behavior of the material was established from photoluminescence studies. The ionization energy (I) and electron affinity (A) were computed from the energy gap values of HOMO and LUMO orbitals respectively. The Molecular electrostatic potentials and Mulliken charges have also been calculated theoretically by applying DFT/B3LYP method. The nonlinear absorption coefficient (β), third order nonlinear refractive index (n 2 ) and third-order nonlinear optical susceptibility (χ 3 ) were calculated from Z-scan measurements, reveals that the grown crystal of 4AADP could serve as a promising source for nonlinear optical devices. © 2018