Hydrothermal carbonization (HTC) is an aqueous-phase procedure to prepare charred material using biomass. To obtain a charred material with high porosity, ash content, and thermal recalcitrance, it is necessary to investigate the influence of HTC conditions (peak temperature, retention time, and feedstock type) on the properties of hydrochar and its derived pyrolysis char (HDPC). Additionally, the relative importance of these conditions for the selected properties was also investigated by heterogeneity index. The results indicated that the properties of both hydrochar and HDPC samples were greatly influenced by the HTC process. The ash content and major metal elements (Na, Mg, K, and Ca) of hydrochar and HDPC samples were strongly influenced by the feedstock type; other properties, such as surface area, carbon sequestration potential, total carbon, total nitrogen, and dissolved organic carbon were moderately influenced by the feedstock type. Overall, this study provided new insights into the relative importance of different HTC conditions in the properties of hydrochar and HDPC samples, which was an important process toward obtaining a "required" charred material for environmental remediation.