The compound preparation, crystallization, spectroscopic characterizations and third order nonlinear optical properties of an organometallic nonlinear optical cesium hydrogen tartrate (CT) single crystal is reported. The title compound was crystallized in orthorhombic crystal system with noncentrosymmetric space group P212121. The functional group and their vibrational states were analyzed by FTIR spectroscopy. The optical band gap was found to be 5.98 eV. The recorded photoluminescence was evident for inter-band defect energy levels in the title crystal. The calculated CIE coordinates on RGB color gamut shows the blue light emitting capacity of CT crystal. Nonlinear optical properties of the title material under continues wave and pulsed laser excitation is reported for the first time. The intensity dependent refractive index (n2), absorption coefficient (β) and third order nonlinear optical susceptibility (χ(3)) of CT under continues wave excitation were found to be 0.569 × 10−8 (cm2W−1), 0.265 × 10−4 (cmW−1) and 8.78 × 10−7 (esu) respectively. The variation of β was studied under pulsed excitation with varying peak intensities. The values were found to be 0.72 × 10−10 (mW−1), 0.68 × 10−10 (m/W−1) and 0.64 × 10−10 (mW−1) for peak intensities of 0.61 × 10−12 (Wm−2), 1.23 × 10−12 (Wm−2) and 2.46 × 10−12 (Wm−2) respectively which confirms the presence of effective two photon absorption in CT. The optical limiting threshold at three intensities mentioned above were found to be 1.36 × 10−12 (Wm−2), 1.55 × 10−12 (Wm−2) and 1.79 × 10−12 (Wm−2) respectively. The value of Meyer’s index (n) by Vickers micro hardness test was found to be 3.74 and it shows CT crystal belongs to soft material category. The thermogravimetric analysis showed that the CT crystal is thermally stable up to 215 °C. The dielectric constant (ε), dielectric loss (tan δ), AC and DC conductivity as a function of frequency and temperature were studied. The superior mechanical, thermal and dielectric properties with intensity tunable optical nonlinearity of cesium hydrogen tartrate single crystal promotes it as a promising candidate for optical limiting application. © 2019, Springer Science+Business Media, LLC, part of Springer Nature.