This study investigates the impact of biodiesel-diesel blends and exhausts gas recirculation (EGR) on the emissions and performance of a single-cylinder, direct injection diesel engine operating at a constant speed of 1600 rpm. Four biodiesel blends—15%, 30%, 45%, and 60% by volume—were tested to evaluate their effects on nitrogen oxide (NOx), hydrocarbon (HC), carbon monoxide (CO), and smoke opacity emissions, as well as engine performance. The results showed that a 45% biodiesel blend at medium load significantly reduced NOx emissions by 65%, highlighting the blend's potential to enhance the renewable fraction of fuel. Further reductions were achieved by applying EGR rates of 15%, 30%, and 40%, leading to a maximum NOx reduction of 81.57% at medium load and 78.22% at high load. While moderate EGR rates (30-40%) slightly increased smoke opacity, levels remained manageable; however, opacity rose sharply beyond these rates for all blends. The study demonstrated that both NOx and smoke emissions could be simultaneously minimized using biodiesel blends and moderate EGR, with only a minor improvement in engine performance. Additionally, the tests indicated a slight reduction in HC emissions and a minimal rise in CO emissions across all blends compared to pure diesel under EGR conditions. Long-term durability tests confirmed the suitability of biodiesel blends (45-60%) for continuous operation without engine modifications or significant wear. This research aligns with global sustainability goals, particularly Sustainable Development Goals (SDGs) 7 (Affordable and Clean Energy) and 13 (Climate Action), by promoting renewable energy use and reducing harmful emissions in diesel engines.