In this study, Tamarindus indica stem fibers and guar gum resin matrix have been used for the production of green composites with varying fiber lengths of 4, 8, and 12 mm and fiber loading of 5%, 10%, and 15 wt%, by hand lay-up process. The green composites were subjected to Fourier transform-infrared spectroscopy, thermal, mechanical, fractography, and water absorption tests as per American Standard Testing of Materials standards. The composites displayed a significant absorption peak at 3303 cm−1, signifying the existence of a hydroxyl group, as indicated by Fourier transform-infrared spectroscopy. The thermogravimetric analysis results showed that the composites were thermally stable up to 225 °C and displayed an endothermic peak at 103 °C. Untreated 4 mm fiber length and 15% fiber loading in the matrix material resulted in superior tensile and flexural characteristics, with values of 23.87 and 33.21 MPa, respectively, compared to other green composites. The composite with a 12 mm fiber length and 5% fiber load exhibited the highest impact resistance, with a load of 75 kJ/mm2, and demonstrated better resistance to water absorption. Furthermore, an eco-friendly flowerpot was developed using the mechanically optimized US0415 green composite material under real-world conditions.