Recently, nanoparticle (NP) synthesis has evolved into a green nanotechnology field, requiring more methods for the eco-synthesis of nanoparticles due to the high costs of other chemical–physical methods. Among the most commonly used nanomaterials, ZnO-NPs are highly valuable due to their specific, thermal, optical, and electronic features. Thus, the main objective of this work was to investigate the green synthesis of ZnO-NPs employing the Phoenix dactylifera L., extract, which is rich in polyphenols, as a reducing agent. In this way, the effect of the concentration of both the precursors and the reducing agent was evaluated. The NPs were characterized and compared through X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and Fourier infrared transformation spectroscopy (FTIR). Additionally, we evaluated the antioxidant properties (TAC and DPPH) and antibacterial activity of these nanoparticles against Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Escherichia coli (E. coli) pathogenic strains. The results show that it is possible to obtain ZnO-NPs using a green reducing agent (polyphenol extract), presenting a particle size between 18.1 and 61.6 nm. In addition, this synthesis highlighted the antioxidant and antibacterial activities of these nanoparticles. In conclusion, this method could be a suitable substitute for typical toxic methods for the synthesis of metallic nanoparticles.