Silver nanoparticles (Ag NPs) were produced from methanol and consecutive aqueous extracts of the underutilized Northeast Indian-grown Hippophae salicifolia leaves and berries. The parameters used in the synthesis process, like extract concentration, AgNO₃ concentration, pH, temperature, and time, were optimized to achieve a higher yield of Ag NPs. PH was the most critical parameter in regulating the size and yield of Ag NPs. Ag NPs were successfully synthesized at optimum conditions and characterized by UV–vis spectrophotometry, DLS, FTIR, XRD, EDX, FESEM, and FETEM. TEM analysis depicted that sea buckthorn leaves and berries extract mediated Ag NPs were monodispersed and spherical with an average particles size of 7.87 ± 2.9 mm to 13.86 ± 5 mm, revealing that Ag NPs synthesized from aqueous extracts are smaller in size than those synthesized from methanol. The synthesized Ag NPs were evaluated for their antioxidant and antibacterial activities. Ag NPs produced from methanol extract of leaves exhibited the highest antioxidant and antibacterial activity of 1.29 ± 0.3 µg/mL and 1.9 µg/mL, respectively. Leaves extract mediated Ag NPs showed better antioxidant activity than pure ascorbic acid in the ABTS assay. Overall, the findings indicate that Ag NPs synthesized from Hippophae salicifolia leaves and berries extract to have significant antioxidant and antibacterial potential for controlling and preventing bacterial infections.