<p>The development of eco-friendly additives for electroplating is essential for advancing sustainable surface engineering. This study reports the synthesis of a novel organic brightener via the condensation of vanillin and L-glutamic acid, both naturally occurring and biodegradable compounds. The synthesized brightener was incorporated into a zinc–nickel (Zn–Ni) electroplating bath to evaluate its effect on coatings deposited on mild steel substrates. The coatings were characterized using field emission scanning electron microscopy (FESEM), reflectance measurements, X-ray diffraction (XRD), and electrochemical impedance spectroscopy (EIS). The results demonstrated that the addition of the brightener significantly reduced surface roughness and increased coating brightness to above 80%, yielding smoother and more uniform surfaces. Enhanced corrosion resistance was also observed, with a corrosion rate of 9.172 × 10⁻⁶ g h⁻¹ compared to 1.135 × 10⁻⁵ g h⁻¹ for coatings obtained from an additive-free bath. Furthermore, the presence of the brightener promoted grain refinement, reducing the average crystallite size from 80.4 to 52.3 nm, and markedly improved surface morphology. Owing to its bio-based origin and low toxicity, the synthesized additive represents a sustainable alternative to conventional synthetic brighteners. Overall, this work supports the advancement of green electroplating technologies and demonstrates a viable approach for producing high-performance, environmentally responsible alloy coatings.</p> Graphical Abstract <p></p>