Food waste is a global issue with significant implications for sustainability. A large portion of food waste results from the rejection of fruits and vegetables due to imperfections or suboptimal sizes, despite their being perfectly edible and nutritious. The fruit of Actinidia arguta, also known as kiwiberry, is rich in beneficial phytochemicals. This makes it an excellent candidate for preventing chronic illnesses and a valuable source of bioactive compounds utilized in health supplements, medical treatments, and beauty products. This study aims to repurpose discarded kiwiberries for the extraction of bioactive compounds, promoting sustainability and maximizing fruit utilization. It focuses on utilizing Response Surface Methodology (RSM) to optimize conditions for ultrasound-assisted extraction (UAE). Subsequently, the impact of three parameters (water-to-ethanol solvent ratio ranging from 0% to 100%; probe amplitude from 30% to 70%; and extraction time from 5 to 30 minutes) on the antioxidant and antiradical properties of the extract was evaluated through TPC, FRAP, ABTS, O2⋅−, HOCl, and ROO⋅ assays. The most effective extraction conditions were achieved with 50% water content, a sonication time of 17.5 minutes, and a probe amplitude of 50%. A comprehensive HPLC-MS analysis of the optimal extract unveiled a total of 22 phenolic compounds, among which chlorogenic acid, neochlorogenic acid, catechin, and epicatechin were the most prominent. Further in vitro cytotoxicity assays demonstrated the extract exhibited no adverse effects on human buccal cell lines HSC-3 and TR146, suggesting its potential safety for oral applications. Overall, this study demonstrates the viability of repurposing kiwiberries to extract bioactive compounds, contributing to sustainability efforts and offering potential applications in functional foods or pharmaceuticals.