This paper reports the synthesis of a cost-effective, stable, and reproducible Boron-doped copper oxide (B–CuO)/Reduced graphene oxide (rGO) binary nanocomposite. A conventional wet chemical synthetic route was used to fabricate the binary nanocomposite. X-ray diffraction (XRD) studies were performed to check the phase purity and crystallinity, scanning electron microscopic (SEM) technique for structural and morphological analysis, energy dispersive spectroscopy (EDX) for surface composition, and Fourier transform infrared spectroscopy (FT-IR) for functional group identification. The experimental results confirmed the formation of the pure nanocomposite. The photocatalytic activity of B–CuO and B–CuO/rGO binary nanocomposite was tested for Methylene blue (MB) dye degradation under sunlight. The B–CuO/rGO binary nanocomposite exhibited improved photocatalytic competence (98%) as compared to B–CuO (85%) in 90 minutes. The antimicrobial activity was measured against four bacterial strains viz. Escherichia coli (E.Coli), Bacillus amyloliquefaciens (B. amyloliquifaciens), Pseudomonas putida (P. putida), Bacillus subtilis (B. subtilis) and one fungal strains Rhizoctonia solani (R. solani). The minimum inhibitory concentration (MIC) was also calculated and it was found that B–CuO/rGO binary nanocomposite exhibited an excellent MIC of 62.2 μg/mL, against the gram-negative E. Coli.