Green synthesised silver nanoparticles (AgNPs) have been identified as a promising new therapy pathway for cancer because of their anti-angiogenic potency. In the present study, CM-AgNPs were biosynthesized using aqueous leaf extract of Cassia marginata Roxb (CM) and were confirmed by spectral studies like UV–Visible and attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopic techniques. The structure and shape of the biosynthesized CM-AgNPs were confirmed by scanning electron microscope (SEM), energy-dispersive spectroscopy (EDX), and high-resolution transmission electron microscopy (HR-TEM) with selected area electron diffraction (SAED) studies. The antioxidant activity of the synthesized nanoparticles were evaluated by 1,1-diphenyl-2-picrylhydrazyl (DPPH) and ferric reducing antioxidant power (FRAP) assay methods, and the IC<inf>50</inf> values were found to be 19.58 ± 1.62 and 742.33 ± 14.57 µg, respectively. The anticancer activity of CM-AgNPs was evaluated against human breast cancer cell lines MCF-7 and MDA-MB-231 by 3-[4,5-dimethylthiazole-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay, and the IC<inf>50</inf> values were found to be 21.02 ± 1.67 and 26.21 ± 0.33 μg/ml, respectively. These results provide promising information about the biosynthesized CM-AgNPs that can be used in the development of novel anticancer drugs. © 2023 Elsevier B.V., All rights reserved.