Lignocellulosic-biomass-derived transparent nanopaper is an emerging substrate or functional component for next-generation green optoelectronics. The fabrication of such transparent nanopaper typically needs the delignification of lignocellulose; however, delignification not only is environmentally unfriendly but also impairs the nanopaper properties such as water stability and UV-shielding capacity. In this study, we present a green and facile lignin modification method instead of delignification to fabricate transparent nanopaper from agro-industrial waste with the combined intriguing properties of lignin and cellulose. Because lignin modification selectively removes chromophores without affecting the bulk lignocellulosic structures, the as-prepared lignocellulose nanopaper (LNP) achieved a comparable optical transmittance (∼90%) but superior UV-blocking ability and haze (∼46%) compared with previously reported cellulose (or delignified) nanopaper. The well-preserved lignin structures endowed the transparent LNP with a low surface energy and a small mesoporous size and volume. In addition to a high thermal stability, the transparent LNP exhibited excellent water stability, evidenced by an up to 103° initial water contact angle, a low equilibrium water absorption (<60 wt %), and a high wet mechanical strength (nearly 40% tensile strength and 92% toughness retained in the wet state). Furthermore, we fabricated a GaAs solar cell with the transparent LNP as an advanced light-management layer that leads to significantly improved power conversion efficiency, even under damp conditions. This work sheds light on the conversion of agro-industrial waste to nanopaper with desirable performances for optoelectronics and brings us a step closer toward the scalable production and application of LNP.