A square-planar Cu(II) complex [Cu(L)Cl], 1, with sterically constrained tridentate phenol-based ligand (HL= N,N,N′-trimethyl-N′-(2-hydroxy-3,5-di-tert-butylbenzyl)-ethylenediamine) with N, N, O donor sites has been synthesized. The complex is characterized by single crystal X-ray diffraction study as well as other spectroscopic techniques. The reported complex crystallizes in monoclinic space group C2/c with a = 30.248(6), b = 13.750(3) and c = 11.410(2) Å with β = 110.232(2)°. The Cu(II) ion adopts a square planar environment in this complex. Electrochemical study of the complex 1 gives quasi-reversible reductive response at E1/2 ≈ −0.5 V due to the reduction of the Cu(II) center along with a reversible oxidation peak at E1/2 ≈ 0.75 V. The oxidation peak arises due to the ligand-based oxidation of phenolate group to phenoxyl radical in the complex. The Cu(II) complex exhibits catechol oxidase activity in methanol as observed by the UV–vis spectroscopy of the aerial oxidation of 3,5-DTBC to 3,5-DTBQ and the reaction proceeds via the formation of ligand phenoxyl radical. The turnover number for complex 1 is 2560 h⁻¹.