Agricultural by-products and Chinese medicine crop residues, as non-traditional animal feed, have great potential to alleviate the scarcity of traditional feed and reduce the environmental burden. In this study, the effects of adding fermented ginseng by-products to the diet on growth performance, meat quality, flavor characteristics and metabolism of Hongyu roosters were evaluated. A total of 100 Hongyu roosters were randomly assigned to either a control (Con) group fed a basal diet or a fermented ginseng by-products (Fe) group fed a basal diet supplemented with 3% fermented ginseng by-products, with five replicates per group, for 100 days. The results demonstrated that the fermented diet significantly enhanced final body weight and average daily gain (ADG) while reducing the feed conversion ratio (FCR) (p < 0.05). The percentages of breast and thigh muscles and breast muscle fiber diameter were significantly increased. The results also exhibited enhanced water-holding capacity, coupled with significantly decreased shear force and drip loss (p < 0.05). Electronic nose and tongue analyses confirmed enriched meat aroma and optimized taste profiles, which aligned with elevated levels of flavor-precursor amino acids and essential polyunsaturated fatty acids. Serum metabolomics found purine metabolism and the biosynthesis of unsaturated fatty acids to be pivotal pathways. Metabolites related to nucleotide and lipid metabolism were regulated. In conclusion, fermented ginseng by-products serve as an effective functional feed to improve poultry growth performance and meat quality.