Global challenges in environmental protection, social welfare, and economic growth necessitate increased energy production and related services. Biofuel production from waste biomass presents a promising solution, given its widespread availability. This study focuses on converting highly potent Carthamus tinctorius L. seed oil (51 % w/w) into sustainable biofuel using a novel, highly reactive, recyclable, and eco-friendly bismuth oxide (Bi2O3) nano-catalyst derived from Cannabis sativa L. leaf extract. The physio-chemical properties of the synthesized biodiesel were analyzed using Gas Chromatography/Mass Spectroscopy (GC-MS), Nuclear Magnetic Resonance (NMR), and Fourier-Transform Infrared Spectroscopy (FTIR). Additionally, the green Bi2O3 nanoparticles were characterized through Scanning Electron Microscopy (SEM), Energy Diffraction X-Ray (EDX), and X-Ray Diffraction (XRD). Optimal conditions for biodiesel production were determined using Response Surface Methodology (RSM) in combination with Central Composite Design (CCD), focusing on molar ratio, catalyst loading, and reaction duration. The highest output (94 %) of C. tinctorius-derived biodiesel (CTBD) was achieved under the following conditions: a temperature (75 degrees C) for time duration (100 min), a methanol to oil ratio (6:1), and a catalyst loading (0.69 wt%). The resulting biodiesel met international standards, with a sulphur content of 0.00097 wt%, and an acid value of (0.34 mg KOH/g). This study demonstrates that converting C. tinctorius waste seed oil into clean bioenergy is an effective waste management strategy that minimizes environmental impact.