The chemistry of mixed ligand transition metal complexes has been of interest of researchers owing to its diverse application and bonding features. Herein, a new thiosemicarbazide derivative namely 1-(2-methyl-3-furoyl)-4-phenyl-3-thiosemicarbazide (HmfpTSC) has been synthesized along with its [Mn(mfpTSC)2(o-phen)] (C1) complex. The prepared ligand (HmfpTSC) and the complex have been confirmed via spectroscopic and single-crystal X-ray data. The HmfpTSC and complex crystallize in a monoclinic crystal system with space group P21/c and P21/n, respectively. HmfpTSC behaves as a uninegative bidentate ligand and its two-unit binds with metal ion along with one unit of o-phen. Using Hirshfeld surface analysis, the weak interactions seen in HmfpTSC and complex have been quantitatively investigated. The MTT assay was used to assess the cytotoxicity of HmfpTSC and [Mn(mfpTSC)2(o-phen)] complex against Dalton's lymphoma cells. Further, the mechanism of anticancer action of ligand and complex was investigated through DAPI, AO/EB staining, and flow cytometry. The both AO/EB and DAPI staining provided compelling evidence of complex-induced cellular and nuclear changes consistent with apoptosis and necrosis.