Biologically derived organic molecules are a cost-effective and environmentally benign alternative to the widely used metal-based electrodes employed in current energy storage technologies. Here, the first bio-derived pendant polymer cathode for lithium-ion batteries is reported. The redox moiety is flavin and is derived from riboflavin (vitamin B-2). A semi-synthetic methodology is used to prepare the pendant polymer, which is composed of a poly(norbornene) backbone and pendant flavin units. This semi-synthetic approach reduces the number of chemical transformations required to form this new functional material. Lithium-ion batteries incorporating this polymer have a 125 mAh g(-1) capacity and an approximate to 2.5 V operating potential. It is found that charge transport is greatly improved by forming hierarchical structures of the polymer with carbon black, and new insight into electrode degradation mechanisms is provided which should be applicable to polymer electrodes in general. This work provides a foundation for the use of bio-derived pendant polymers in sustainable, high-performance lithium-ion batteries.