We report a sustainable approach to synthesize silver nanoparticles (SNPs) using a bio-inspired method employing Lagerstroemia speciosa fruit extract. Characterized SNPs exhibited a spherical morphology with a hydrodynamic diameter of 61.12 nm and a face-centred cubic crystalline structure confirmed by XRD with a prominent peak at 38.79°. The synthesized SNPs displayed a UV-visible absorption peak at 423 nm, indicating the formation of metallic silver. Zeta potential measurements revealed a value of −10.9 mV, suggesting good colloidal stability. FTIR analysis confirmed the involvement of biomolecules in SNPs synthesis and stabilization. These greenly synthesized SNPs demonstrated efficient catalytic degradation of Rhodamine B and Malachite Green dyes, with degradation rates of 0.2193 min−1 and 0.3636 min−1, respectively, following first-order kinetics. This study highlights the potential of plant-mediated SNPs as a promising catalyst for the remediation of dye-contaminated water.