This study evaluated the effects of dietary supplementation with single-cell protein (SCP) by-product derived from a lysine fermentation on growth performance, nutrient digestibility, organ development, excreta characteristics, and meat quality in broiler chickens. A total of 630 one-day-old Ross 308 broilers were randomly assigned to diets containing 0, 1, 3, 5, or 7% SCP for 35 days. Growth performance indicators, including body weight gain, feed intake, and feed conversion ratio, were not significantly affected by SCP inclusion throughout the experimental period (P > 0.05). Similarly, the apparent digestibility of dry matter, nitrogen, and energy, as well as the relative weights of the heart, crop, gizzard, proventriculus, liver, kidney, spleen, and bursa of Fabricius remained unchanged (P > 0.05). No differences were observed in excreta gas emissions, excreta consistency, or breast meat quality parameters such as pH, colour, water-holding capacity, cooking loss, and drip loss. Overall, these results demonstrate that SCP can successfully replace conventional soybean meal in broiler diets without negative effects on performance, nutrient utilisation, physiological development, or meat quality. Collectively, the findings highlight the potential of SCP as a sustainable and efficient alternative protein source in poultry production.