Visible laser irradiation is utilized to transform an insulating film containing jellyfish biomass (JF) and silicon nanoparticles (SiNPs) into a conductive 3D porous carbon network that encapsulates the nanoparticles. The conductive carbon matrix improves contact between the electrolyte, current collector, and active substances while using its porosity as a buffer to reduce the impact of silicon volume expansion on mechanical stability. Jellyfish-based laser-induced 3D porous carbon-SiNP (JF/SiNP) thin composite anodes display outstanding cyclic stability (>1000 cycles), excellent capacity retention (>50% retention after 1000 cycles), exceptional coulombic efficiency (>99%), superb reversible gravimetric capacity (>2000 mAh/g) and high rate performance capability (>1.6 A/g). Along with exhibiting phenomenal electrochemical performance, our fully sustainable synthesis uses an environmentally remediating and economically feasible carbon precursor that is virtually unprocessed, devoid of binders, conductive additives, expensive or hazardous solvents, and is conducted at low-energy consumption, room-temperature conditions. As a proof of concept, green synthesis of whole jellyfish-based composite anodes is presented as a blueprint for use of a wide range of sustainable carbon precursors into next-generation lithium-ion batteries. Equally significant is the potential that widespread utilization of jellyfish biomass has for environmental remediation and restoration of imperiled marine ecosystems. This approach represents an unparalleled paradigm for sustainability compared to use of traditional "sustainable" materials that, at best, have negligible environmental benefits.