This article proposes two novel bio-fibrils from agricultural waste and agro-industrial waste as particulate reinforcement in polymer composites. Microfibrils were extracted from the peels of Phaseolus lunatus and Vigna radiata. The main aim of this work is to valorize the obtained fibrils as fillers in polymer composites. The fibrils were subjected to physio-chemical, thermal, and morphological characterization. The physio-chemical analysis revealed that the Phaseolus lunatus consisted of 65.2% of cellulose and 20.1% of hemicellulose contents, whereas the Vigna radiata possessed 58.2% of cellulose and 21.9% of hemicellulose contents respectively. It is well known that the density of the fibril influences the weight of the composites. The density of Phaseolus lunatus and Vigna radiata fibrils were found to be 0.46 and 0.53 g/cm3. Thermogravimetric analysis revealed that both the fibrils exhibited a thermal stability of more than 300 °C. Hence, with better functional characteristics, the novel fibrils can be a potential reinforcement in polymer composites for lightweight applications.