Despite proposed alternative fuels in the recent past, the race for a natural substitute still exists. In this research work, we suggest biodiesel preparation from the rarely explored macroalgae D. dichotoma using a supercritical fluid system of ethanol/ THF. Reduced graphene oxide was prepared using dried jasmine powder as bio-reductant. Reduced graphene oxide was sulphonated using sulfanilic acid, and the catalysts were characterized by XRD, BET surface area, FTIR, and SEM techniques. The reaction conditions for algal oil conversion into biodiesel in supercritical ethanolysis were optimized. FTIR, and GCMS were eployed as analytical tools to analyze the produced biodiesel. The optimized reaction conditions were 265 °C, ethanol: algal oil= 15:1, Reaction time = 10 min, catalyst loading = 5% GO, and THF: ethanol −0.4 for 78% FAEE yield using GO. 10 wt% S-rGO yielded a maximum of 89% FAEE; and 22.55% C18:2. The catalyst was efficient till five cycles. The work assures the utility of abundant macroalgae for alternative fuel production.