The rising demand for fossil fuels and the exploration of renewable energy sources from plants have gained significant attention due to their role in reducing emissions and enhancing energy security. Prosopis juliflora, abundantly available in India, offers a viable source for biodiesel production. This study investigates the performance and emission characteristics of a 5.2 kW, 1500 rpm, four-stroke single-cylinder compression ignition (CI) engine using blends of diesel, vegetable oil, and biodiesel derived from Prosopis juliflora seeds. The engine was tested with pure diesel, vegetable oil (PJO), biodiesel (B100), and biodiesel-diesel blends at 20%, 40%, 60%, and 80% by volume, designated as B20, B40, B60, and B80, respectively. Key performance metrics, including brake thermal efficiency (BTE) and brake specific energy consumption (BSEC), were measured, along with emissions such as carbon monoxide (CO), smoke, hydrocarbons (HC), and nitrogen oxides (NOx). Results indicated that BTE for B20 was comparable to diesel, with values of 30.52% and 30.68%, respectively, at 5.2 kW. The BSEC for B20 was recorded at 11.79 MJ/kWh compared to 11.74 MJ/kWh for diesel. Emission analysis revealed that HC and smoke emissions were lower for all biodiesel blends compared to diesel. At 5.2 kW, HC emissions were 74 ppm for B20 versus 75 ppm for diesel, and smoke emissions were 67.7% for B20 compared to 69.1% for diesel. However, NOx and CO emissions were slightly higher for biodiesel blends. This study suggests that Prosopis juliflora-derived biodiesel can effectively reduce HC and smoke emissions while maintaining performance, highlighting B20 as a promising alternative to conventional diesel fuel.