Fresh-cut fruits, renowned for their convenience and nutritional value, are susceptible to rapid deterioration, compromising their quality and shelf life. In this study, a sustainable and environmentally friendly edible coating was developed based on sodium alginate (SA; 1% w/v), cedar mucilage (CM; 4% w/v), and calcium chloride (2% w/v), applied using a layer-by-layer technique to preserve the quality and prolong the shelf life of fresh-cut melon. Fruits were cut into cubes coated or uncoated by dipping and subsequently packaged in a polyethylene terephthalate container and stored for 15 days at 4 °C. Physicochemical traits and qualitative features such as polyphenol, flavonoid, carotenoid, ascorbic acid content, as well as antioxidant activity, were assessed. Furthermore, the enzymatic antioxidant system and the ascorbate–glutathione cycle were investigated. The coating reduced weight loss and enhanced polyphenol, flavonoid, and ascorbic acid content and antioxidant activity during cold storage. Edible coating (SA + CM) represents a valid tool to extend the postharvest life, improve the storability, and enhance the physicochemical and qualitative traits of fresh-cut melon. Further research is required to optimize coating formulations and application techniques to maximize their effectiveness and commercial viability in the food industry.