The growing demand for healthier foods and sustainable production practices has accelerated research into the valorization of agro-industrial by-products as functional food ingredients. Plums (Prunus domestica L.) are highly valued for their rich chemical composition and nutritional qualities, as well as for the health-promoting effects attributed to their bioactive compounds. This study examines the sustainable utilization of dried plum pomace (DPP), a fiber- and antioxidant-rich byproduct of juice processing, in the development of nutrient-enriched dairy products. Different levels of DPP powder (10% and 20%) were incorporated into whey cheese matrix to assess its impact on nutritional quality, physicochemical, phytochemical, color, textural characteristics, and sensory acceptance. The addition of DPP significantly increased the total dietary fiber and total anthocyanin content (42.57–66.20 mg C3G/ 100 g of dw), enhancing the antioxidant potential (680.25–888.63 μmol TE/g dw) of the DPP-supplemented dairy product. Sensory evaluation indicated that moderate levels of DPP (10%) provided improved flavor complexity, slight color intensification, and good consumer acceptability. The findings demonstrate that dried plum pomace can serve as an innovative, sustainable ingredient for developing value-added functional dairy products, simultaneously contributing to circular economy principles and improved consumer nutrition.