The present study embarks the concept of developing continuous biohythane (biohydrogen followed by biomethane) production from renewable energy sources. Combination of sugarcane bagasse and water hyacinth were used to reduce the use of costly chemicals for fermentation process. The lignin content of sugarcane bagasse was reduced using alkaline hydrogen peroxide pretreatment. The maximum lignin reduction of 89 ± 3% (w/w) was observed at 50 °C and 150 min pretreatment time. Scanning electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopy analysis were performed to confirm the lignin removal after pretreatment. Further, the influence of the hydraulic retention time on two stage biohythane production was studied by using combination of pretreated sugarcane bagasse and water hyacinth (1:2 ratio) (soluble COD, 30 ± 2 g/L) in continuous stirrer tank bioreactor. The suitable hydraulic retention time for biohydrogen and biomethane production were found to be 8 h and 10 d, respectively, which gave the maximum hydrogen and methane yield of 303 mL/g COD and 142 mL/g COD, respectively. The continuous biohythane production process increased the overall substrate conversion efficiency up to 86% with the maximum gaseous energy recovery of 8.97 kJ/g COD.