The chemistry of biologically active thiosemicarbazide has been of interest to researchers owing to its diverse application and bonding features. In the present study, a new thiosemicarbazide derivative namely 1-(4-nitrobenzoyl)-4-phenyl-3-thiosemicarbazide (HnbphTSC) has been prepared and along with its [Ni(nbphTSC)2(en)]·CHCl3 (1) complex. The prepared ligand (HnbphTSC) and complex 1 have been characterized through spectroscopic and single-crystal X-ray data. The HnbphTSC and complex 1 crystallize in triclinic and monoclinic crystal systems with space groups P1¯ and P21/C, respectively. The weak interactions present in HnbphTSC and complex 1 have been quantitively studied through hirshfeld surface analysis. The physiochemical characteristics of HnbphTSC and complex 1 are also verified using DFT calculations, and the resultant results are in strong agreement with the experimental findings. The HOMO and LUMO energy gap have been calculated as 3.160 eV and 2.212 eV for HnbphTSC and complex 1, respectively. MTT assay was used to evaluate the cytotoxicity of HnbphTSC and complex 1 against Dalton's lymphoma (DL) cells. We further assessed the mode of tumor cell death and the drug's effect on nuclear condensation and plasma membrane integrity by employing DAPI/PI dual staining technique.