Carbon materials are on the rise owing to their outstanding properties compared with their metal-based homologs. This interest triggered intensive research toward the preparation of carbon-based nanostructures including those doped with heteroatoms, among which nitrogen-containing carbon materials are the most ubiquitous. Biomass and biowastes stand as sustainable and cost-effective precursors to access tunable carbon-based nanomaterials. Excitingly, chitosan—an aminopolysaccharide marine waste—displays additional advantages of distinctively featuring nitrogen in the biopolymer skeleton, thereby avoiding the tedious step of nitrogen enrichment of the carbonaceous framework that often necessitates the use of exogenous chemicals. This review sheds light on the opportunities offered by transforming chitosan into nitrogen-containing carbon framework, including porous carbon, graphene, and carbon dots derivatives. The templating effect of chitosan, its strong interaction with metal species, and its shaping in different forms provide multifaceted possibilities for the rational design of advanced functional carbon nanomaterials. Overall, this fashionable trend in material science is expected to trigger a new debate around the most efficient way in which biomass and biowastes should be transformed, sustainability could be improved, and high-value added materials could be obtained.