The utilization of biomass as a sustainable and renewable resource for nanomaterial synthesis has received considerable attention in recent years. Through the efficient utilization of biomass waste, opportunities for energy production, energy conversion, and the fabrication of nanomaterials can be maximized. The combination of biomass‐based nanomaterials with additional nanomaterials makes the composite system have more remarkable performance, which further facilitates the transformation procedure of biomass‐based nanomaterials for applications. This comprehensive review provides an overview of the preparation and applications of biomass‐based nanomaterials. The preparation section covers a range of methods for synthesizing biomass‐based nanomaterials, including biomass‐based carbonaceous nanomaterials, biomass‐based carbon nitride nanomaterials, nanomaterials derived from biomass templates, biomass‐based nanomaterials as carriers, and the use of biomass for metal ion reduction. The applications section explores the diverse applications of biomass‐based nanomaterials, such as hydrogen production, carbon dioxide reduction, batteries, and supercapacitors. The unique properties and advantages of biomass‐based nanomaterials in each application are discussed. The conclusion summarizes the current progress and presents future perspectives for the development and utilization of biomass‐based nanomaterials. This review emphasizes the potential of biomass as a valuable and sustainable source for nanomaterial synthesis, opening up promising opportunities in various fields.