Introduction Breast cancer is the most common type of cancer among women, and despite the current therapeutics, patient survival remains unsatisfactory. Furthermore, due to the side effects of these traditional treatments (such as surgery, chemotherapy, and radiotherapy), there is an urgent need for innovative strategies in the treatment of breast cancer. Green-synthesised nanoparticles (NPs) are among the most promising new approaches. Therefore, in this study, we aimed to describe the biofabrication of silver nanoparticles (AgNPs) using Betula pendula Roth leaf extract (Bp.E) and evaluate their selective biological effects on MCF-7 and MCF-12A cell lines. Methods The purity, size, and shape of biosynthesized AgNPs with Bp.E were characterised using Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), and X-ray diffraction (XRD). The selective anticancer potential of AgNPs was detected using the XTT assay. Results The anticancer activity of nanoparticles containing aromatic (C C, –CH) and plant-derived phenolic –OH groups and characterised as having a spherical structure with an average size of 32 nm was evaluated by the XTT method. The synthesised AgNPs exhibited a higher cytotoxic effect on MCF-7 than Bp.E. Furthermore, the synthesised AgNPs were determined to show selective cytotoxic activity against cancer cells compared to healthy cells. Conclusion In conclusion, the synthesised AgNPs represent a cost-effective and environmentally friendly biomaterial candidate, with clear potential for evaluation as an anticancer agent. Moreover, the findings will highlight further studies using various cancer cell lines and in vivo models of the therapeutic potential and safety of this biomaterial.