Feeding low crude protein (LCP) diets supplemented with crystalline amino acids improves environmental and welfare parameters of broilers. However, increased body fat contents in broilers fed LCP diets have become a concern. Black soldier fly larvae oil (BSFLO), rich in lauric acid, has been reported to inhibit lipogenesis and reduce body fat. A 3 × 2 factorial experiment was conducted to evaluate the effect of BSFLO on performance, blood biochemistry, carcass quality, fat metabolism gene expression, and litter quality in broilers fed protein-reduced diets. A total of 288 broilers were divided into 6 treatments: three CP levels (200, 185, or 170 g/kg; high [HCP], medium [MCP], or low [LCP]) and two oil sources (BSFLO and Crude Palm Oil [CPO]), with 6 replicate pens of 8 birds each. Results showed a 15 g/kg CP reduction had no effect on body weight and feed intake (P > 0.05) but increased FCR (P = 0.001). A 30 g/kg CP significantly reduced the body weight and feed intake with inferior FCR (P < 0.05). However, negative effect of low CP diets on FCR was mitigated by BSFLO (P = 0.008). Reducing CP by 30 g/kg increased fat pads (P = 0.033), whereas BSFLO reduced fat pads (P = 0.049) at all three CP levels. Protein-reduced diets increased blood cholesterol (P = 0.002), HDL (P < 0.001), and LDL (P = 0.002). BSFLO decreased blood triglyceride (P = 0.026) and cholesterol (P < 0.001). Reducing 30 g/kg CP increased meat cooking loss (P = 0.035), while BSFLO decreased cooking loss (P < 0.001). BSFLO increased meat protein (P < 0.001) and decreased cholesterol (P = 0.003). The inclusion of BSFLO in protein-reduced diet down-regulated the gene expression of FAS, ACC, SREBP-1, and HMGR in broilers (P < 0.001). Reducing CP levels decreased litter pH (P = 0.011), nitrogen (P < 0.001), ammonia (P < 0.001) and moisture (P = 0.018). The study concludes that BSFLO reduced body fat by down-regulating the lipogenesis gene expression. In addition, BSFLO enhanced feed efficiency in broilers fed protein-reduced diet.