The green synthesis of inorganic nanoparticles using plant extracts has been an important strategy to mitigate the uses of hazardous chemicals and thus reduce toxic by-products. We herein report for the first time the synthesis of silver nanoparticles (AgNPs) utilizing Vitis heyneana fruit peel as a key agent. Specifically, oleanolic acid was found in the extract and its crucial role as both reducing and stabilizing agent was experimentally evidenced. The as-synthesized AgNPs were morphologically and structurally characterized to possess quasi-spherical shapes with an average diameter of 11 nm and exhibit polycrystalline nature. Bioactive studies indicated that as-synthesized AgNPs revealed potent antimicrobial activities against Lactobaccillus plantarum, Pseudomonas aeruginosa, and Aspergillus flavus, demonstrating an IC50 value of 20.00 ± 2.05 μg ml−1 and a MIC value of 32 ± 0.03 μg ml−1 (against Pseudomonas aeruginosa); the NPs also possessed superior antioxidant activities with an IC50 value of 23.22 ± 1.25 μg ml−1 compared to vitamin C (18.23 ± 0.15 μg ml−1). The AgNPs further revealed capabilities of colorimetrically detecting Hg2+ ions with a limit of detection of 0.048 μM and a limit of quantitation of 0.16 μM. These findings therefore suggest promising uses of the phytosynthesized AgNPs in nanomedicine and sensing technology.