6-mercaptopurine (6-MP) is used for treating various cancers and autoimmune disorders. A few examples of transition metal complexes of 6-MP have been shown to enhance its anticancer activity, but many remain untested. We isolated five highly stable and colored metal complexes of 6-MP and confirmed their structures by elemental analysis, spectral, and thermal techniques. Infrared (IR) spectra revealed that 6-MP is a bidentate ligand that interacts through sulfur and pyrimidine nitrogen in a 1:2 (M:L) molar ratio. The magnetic susceptibility and electron paramagnetic resonance (EPR) spectra for the Cu(II) complex revealed an octahedral arrangement around the metal ion with strong covalent bonding. The fully optimized geometries of the metal structures obtained using density function theory (DFT)/B3LYP calculations were used to verify the structural and biological features. DNA titration revealed that the octahedral Cu(II) complex has a critical binding constant value of Kb = 8 × 105. Docking studies using three different cancer protein receptors were used to predict the biological applications of the synthesized drug-metal complexes. Finally, cytotoxicity assays against a myeloma cancer cell line (MM) and a colon cancer cell line (Caco-2) revealed favorable anticancer activity for the copper complex, exceeding that of the gold-standard chemotherapeutic cisplatin.