Silver selenide (Ag2Se) is a promising nanomaterial due to its outstanding optoelectronic properties and countless bio-applications. To the best of our knowledge, we report, for the first time, a simple and easy method for the ultrasound-assisted synthesis of Ag2Se nanoparticles (NPs) by mixing aqueous solutions of silver nitrate (AgNO3) and selenous acid (H2SeO3) that act as Ag and Se sources, respectively, in the presence of dissolved fructose and starch that act as reducing and stabilizing agents, respectively. The concentrations of mono- and polysaccharides were screened to determine their effect on the size, shape and colloidal stability of the as-synthesized Ag2Se NPs which, in turn, impact the optical properties of these NPs. The morphology of the as-synthesized Ag2Se NPs was characterized by transmission electron microscopy (TEM) and both α- and β-phases of Ag2Se were determined by X-ray diffraction (XRD). The optical properties of Ag2Se were studied using UV–Vis spectroscopy and its elemental composition was determined non-destructively using scanning electron microscopy–energy-dispersive spectroscopy (SEM–EDS). The biological activity of the Ag2Se NPs was assessed using cytotoxic and bactericidal approaches. Our findings pave the way to the cost-effective, fast and scalable production of valuable Ag2Se NPs that may be utilized in numerous fields.