Agriculture, particularly modern, high-input farming systems, constitutes the backbone of food and nutritional security globally. The disposal of agricultural waste (the byproducts and leftovers generated from crop farming and food production industries) has emerged as one of the prime challenges recently. Among these, bio-economical disposal methods for crop residues such as straw, husks, and stalks (rice straw, wheat husks, corn stalks), leaves, pruning from fruit trees and vineyards, and spoiled or damaged crops hold pertinence to reduce environmental degradation caused by their open field burning. Chemical engineering approaches such as hydrothermal carbonization (HTC) that entail dehydration and decarboxylation to enhance the carbon content of biomass, thereby increasing its calorific value, have been developed to transform waste into different useful products. This review study critically evaluates the advances in the valorization of agricultural wastes into marketable products using the HTC technique. Moreover, the limitations of the HTC technique, its prospective employment, and future research needs have been objectively highlighted.