As the construction industry shifts toward more sustainable solutions, bio-based materials are emerging as promising alternatives to conventional building components. This work explores two primary categories: supplementary cementitious materials (SCMs) derived from agricultural byproducts, and natural fibers used to reinforce cement-based composites. Materials such as rice husk ash and sugarcane bagasse ash can partially replace Portland cement, lowering carbon emissions while maintaining structural performance. At the same time, plant and animal-based fibers like jute, sisal, coconut, and wool enhance mechanical properties such as tensile strength and crack resistance. The use of renewable biopolymers and bio-based phase-change materials further improves workability, insulation, and energy efficiency. While challenges such as durability and material variability remain, bio-based materials offer a compelling pathway toward greener, eco-efficient construction.