The agro-industry significantly contributes to organic solid waste. Fruits and vegetables show a short shelf life and are the most wasted, with peels, husks, and seeds being the primary waste. Scientific research now focuses on revalorizing this organic waste by extracting active compounds such as polyphenols. This promising research is a significant step toward a more sustainable and circular economy, offering a hopeful future for waste management in the agro-industry. However, polyphenol extraction is a complex and critical step due to the variability and complexity in solubility, chemical structure, and quantity, and the absence of a standard extraction protocol presents significant challenges. This review focuses on the polyphenol type and quantity obtained by “green nonconventional” extraction techniques from agro-industrial wastes, describing the principal green techniques and the parameter conditions that influence polyphenol extraction. Waste valorization offers new opportunities for polyphenol recovery and can have significant applications and challenges in the food industry. These compounds, known for their antioxidant, antimicrobial, and anti-inflammatory properties, can formulate new functional food products and additives/ingredients, inspiring innovation in the food industry and apport sustainable development.