Coupling the diazonium salt of sulfadiazine with dibenzoylmethane afforded the 4‐(2‐(1,3‐dioxo‐1,3‐diphenylpropan‐2‐ylidene)hydrazinyl)‐N‐(pyrimidin‐2‐yl)benzene sulfonamide ligand (HL). The ligand (HL) and its Cu(II) complex structure have been investigated via magnetic attraction testing, TGA, FTIR, UV–visible, XRD, and CHN analyses. The spectrum data indicate that the ligand demonstrates monobasic bidentate behavior via deprotonating opposite the oxygen atom of the carbonyl (CO) group and linking using the NH of the hydrazone group (NNH). Copper (II) complex present in octahedral structure. A number of TGA steps (Ea, A, ΔH*, ΔS*, and ΔG*) had their dynamical characteristics computed and described using the Coats–Redfern and Horowitz–Metzger formulas. Molecular studio programmer was utilized to perform density functional theory (DFT) calculations in order to investigate the ideal configuration of HL and its Cu(II) complex. The HL and its copper (II) complex exhibited antitumor effects against MCF‐7 and HepG‐2 cell lines. Furthermore, the width of the inhibition zone was employed to evaluate the in vitro antibacterial effect of HL and a specific complex towards Gram‐negative organisms Escherichia coli (E. coli) and Gram‐positive organisms Staphylococcus aureus. The ligand and its Cu(II) complex were examined using both the viscosity and spectrum of absorption of calf thymus DNA binding experiments.