Photothermal energy conversion represents a cornerstone process in the renewable energy technologies domain, enabling the capture of solar irradiance and its subsequent transformation into thermal energy. This mechanism is paramount across many applications, facilitating the exploitation of solar energy for different purposes. The photothermal conversion efficiency and applications are fundamentally contingent upon the characteristics and performance of the materials employed. Consequently, deploying high-caliber materials is essential for optimizing energy capture and utilization. Within this context, photothermal nanomaterials have emerged as pivotal components in various applications, ranging from catalysis and sterilization to medical therapy, desalination, and electric power generation via the photothermal conversion effect. This review endeavors to encapsulate the current research landscape, delineating both the developmental trajectories and application horizons of photothermal conversion materials. It aims to furnish a detailed exposition of the mechanisms underlying photothermal conversion across various materials, shedding light on the principles guiding the design of photothermal nanomaterials. Furthermore, addressing the prevailing challenges and outlooks within the field elucidates potential avenues for future research and identifying priority areas. This review aspires to enrich the understanding of photothermal materials within the framework of energy conversion, offering novel insights and fostering a more profound comprehension of their role and potential in harnessing solar energy.