Pyrolysis was considered as a key approach for high-value utilization of biomass; however, conventional pyrolysis was primarily targeted at bio-oil, while biochar was regarded merely as a low-value byproduct, which made full-component valorization of feedstocks difficult to achieve. Luffa sponge was found to be rich in cellulose and hemicellulose, possessed well-developed pores and strong liquid absorption capacity, and exhibited dual characteristics as both a precursor for furan compounds and a porous carbon material. Based on this, ammonium bisulfate (NH4HSO4) was proposed as a bifunctional reagent to enhance the selective production of furan compounds during luffa sponge pyrolysis, which was followed by the cascading transformation of the resulting biochar into nitrogen-doped supercapacitor carbon materials. The catalytic effects of four different salt loadings were compared, and the influences of NH4HSO4 loading ratio and pyrolysis temperature were systematically investigated. The results showed that abundant acidic sites were provided during luffa sponge pyrolysis by the strong acidity of NH4HSO4 and its retained active component—ammonium pyrosulfate ((NH4) 2S2O7)—at 350℃, which promoted the dehydration and isomerization of sugars to generate furan compounds. Under conditions of an NH4HSO4/luffa sponge mass ratio of 1∶1 and a pyrolysis temperature of 350℃, a furan compound (FF+5-MF) yield of 3.27% was achieved. After activation, the specific surface area of the obtained biochar was significantly increased from 511.1m2/g to 2009.7m2/g, and the nitrogen content was raised from 0.88% to 5.74%. Furthermore, the specific capacitance was improved by approximately 90.9% to 212.1F/g at 1A/g, and a capacitance retention rate of 76.1% was obtained at 10A/g.