The use of additives to modulate metal electrodeposition from deep eutectic solvents has, to date, apparently been of little interest given the dearth of such studies in the literature. Here, we have actively investigated the effects of nicotinic acid (NA) on the electrodeposition of copper in a choline chloride (ChCl)-ethylene glycol (EG)-based deep eutectic solvent (DES), (1ChCl:2EG), considered a “green solvent” due to its physiochemical properties. Bright copper deposits were formed when NA was added to the Cu electrolyte, while a dull Cu deposit was produced in its absence. New Cu species were found to have formed in the 1ChCl:2EG-based liquid when NA was added to the electrolyte. A number of analytical techniques, in this instance cyclic voltammetry, chronoamperometry, and chronocoulometery, have been employed to determine the various electrochemical properties, nucleation mechanisms, and kinetics of the Cu species reported herein. The diffusion coefficient for the Ethaline-Cu system was found to be affected by the concentration of NA. An electrochemical quartz crystal microbalance (EQCM) was used to monitor the current efficiency of the copper deposition in both systems. The morphologies, thicknesses, roughness, and crystal structures of the copper electrodeposited from the NA-modified electrolyte were characterised via scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray diffraction (XRD), which between them demonstrate that the NA introduced into this system acts as a highly effective brightener, producing highly uniform and smooth copper deposits.