The ligand 5-Methyl-2-phenyl-4-(1,3-thiazol-2-yl)-2,4-dihydro-3H-pyrazol-3-one (MPP) has been synthesized via Sandmeyer reaction of MPP with 2-aminothaizole. A series of complexes of the ligand with Co(II), Ni(II), Cu(II) and Zn(II) ions are synthesized and structurally characterized by Proton Nuclear Magnetic Resonance (1H-NMR), Infra-Red (IR), UV-Visible and Powder X-ray Diffraction (PXRD) spectral techniques. The powder XRD studies reveal that all complexes are in crystalline nature. The cytotoxic activity of the complexes and the uncoordinated ligand against human breast cancer (MCF-7) and chronic myelogenous leukemia cell line (K-562) exhibits good viability in the range of 50.16-55.16% at a concentration of >100-110 µg/ml as compared to the inhibition in the untreated cells. Further, the metal complexes and the ligand were screened for the antibacterial activity, the cytotoxicity studies are correlated with computational docking analysis.