Lignocellulosic biomass conversion has been researched as a potential alternative to bio-building blocks, platform chemicals, and value-added commodities due to being a renewable feedstock with lower environmental impact than fossil fuels. As food security is arguably a major challenge in the twenty-first century, researchers focus their efforts in the agricultural waste to reduce the world’s dependence on fossil fuels, while avoiding the use of human food sources and capitalizing on environmentally harmful by-products. Sub-supercritical water hydrolysis has the potential to decompose macromolecules, such as cellulose, hemicellulose, and lignin into monomeric sugars and low-molecular weight substances and valuable intermediate products for pharmaceutical, fuel, textile, and construction industry with several advantages over conventional processes; water is nontoxic and works as a solvent for a wide range of products due to the temperature effect on its characteristics (density, dielectric constant, ionic product). This review provides an overview of the state of the art in hydrolysis with sub-supercritical water in the context of recovering compounds from food processing waste and agricultural substrates.