The study evaluated the potential of defatted black soldier fly larvae meal (BSFLM) as a sustainable alternative to fish meal (FM) in Nile tilapia (Oreochromis niloticus) diets while promoting organic waste valorisation through a circular economy approach. Black soldier fly larvae (BSFL) (Hermetia illucens) were reared on faecalsludge and organic waste, harvested at the pre-pupal stage, and defatted to produce a protein rich feed ingredient. Three isonitrogenous diets (30 % crude protein) were then formulated such that BSFLM substituted FM at 0% (control, diet 1), 50% (diet 2) and 100% (diet 3) on a protein basis. Nutritional chemical analysis on ingredients and diets were determined while diets’ fatty acids profile was determined by MPA FT-NIR spectrometer. The analysis showed significant differences (p < 0.05) among the diet treatments for all measured parameters except dry matter. FM registered the highest crude protein, (57.89%) followed closely by defatted BSFL (54.69%). However, partial substitution of FM with defatted BSFL in diets increased crude protein levels (31.77%), registered moderate crude fat (5.26%) and moderate crude fibre (11.08%) (diet 2) levels compared to FM meal diet (diet 1). Consequently, partial substitution yielded the highest overall polyunsaturated fatty acids (ƩPUFAs) content (4.81 mg/g). Thus, the study shows that, partial replacement (50%) of FM with defatted BSFLM provides rich proximate and fatty acid profiles that can support Nile tilapia production while sustainably managing waste, promoting resource recovery within a circular economy.