The green fabrication of biocomposites from agricultural waste, such as bagasse, is critical for promoting sustainable material utilization and reducing carbon emissions. However, developing high-performance, multifunctional biocomposites without external adhesives remains a considerable challenge. In this study, we engineered a glueless biocomposite by integrating bagasse fibers with intrinsic lignin liberated through a low-alkalinity geopolymer pretreatment process. The pretreatment facilitated the release of intrinsic lignin, which underwent a glass transition (Tg) during hot pressing at 140 °C for 30 min. This Tg transformation allowed lignin to function as a natural adhesive, forming robust fiber bonds through hydrogen bonding and enhanced chemical interactions. The resulting biocomposite exhibited excellent mechanical properties, achieving a flexural strength of 26.81 MPa and a flexural modulus of 3.31 GPa, which represent increases of 298.93 % and 147.46 %, respectively, compared to untreated materials. These values exceed the thresholds of China's P4 grade standard for general-purpose particleboards. Beyond its strength, the biocomposite exhibited superior hydrophobicity (water contact angle of 98.98°), thermal stability, and retained performance after three recycling cycles, underscoring its potential as a sustainable substitute for resin-bonded composites. Additionally, assessments of the environmental impact of the biocomposites and the mechanical and electrochemical properties of the conductive monolithic carbon obtained via pyrolysis demonstrated excellent performance, giving it a highly competitive edge in the market.