Plant-derived smart nanomaterials offer an eco-friendly and sustainable means for replacement of standard synthetic nanomaterials. These materials, derived from natural sources, possess unique properties and can intelligently respond to environmental stimuli such as pH, temperature, and light. Plant-derived nanomaterials, i.e., cellulose nanofibers, lignin nanoparticles, and biopolymers, with biodegradability, biocompatibility, and non-toxic characteristics, are of interest to researchers because of their ability to absorb liquids, store electricity, control diffusion, self-assembly, and other properties at the nanoscale. This chapter discusses the various plant-based nanomaterials, their synthesis methods, and the critical smart properties that allow them to be used as smart materials. It also considers their multiple uses in fields including drug delivery, environmental sensing, agriculture, and food packaging, where their responsiveness is crucial. Furthermore, the chapter discusses these nanomaterials’ synthesis procedures, functionalization approaches, and characterization methods systematically. Their renewable origin not only supports environmental sustainability but also provides a diverse range of structural and chemical features that can be fine-tuned during synthesis. This tunability allows customization of key properties such as particle size, surface functionality, and responsiveness, making them suitable for integration into a variety of systems. Finally, the chapter discusses the challenges and the potential of plant-based smart nanomaterials to be developed and commercialized.