Copper(II) and nickel(II) mixed ligand complexes were synthesized from 4-methoxysalicylaldehyde-N-phenylthiosemicarbazone and 3,5-lutidine. The structures of the complexes have been characterized by elemental analysis, IR, UV, 1H NMR and ESI-MS spectra, together with magnetic susceptibility measurements. Complex I was found to have a distorted square planar geometry, with coordination of azomethine nitrogen, thiolate sulfur, phenolate oxygen and pyridyl nitrogen atoms, by the single-crystal X-ray diffraction technique. Quantum chemical DFT calculations have also been carried out using the DFT/HSEH1PBE method with the cc-pVDZ basis set for C, H, N, O and S atoms, and the LANL2DZ basis set for the metal atom. The antioxidant activities of the ligand and its metal complexes were investigated by CUPRAC and DPPH assays and calculated as their trolox equivalent antioxidant capacities (TEAC). Electrochemical properties were performed with cyclic voltammetry and square wave voltammetry. Both the ligand and its metal complexes were found to have antioxidant capacity.