One of the economically most interesting methods is to use commercial catalysts such as silicon, alumina, and zeolite-based catalysts in biomass Hydrothermal Liquefaction (HTL). Literature on the HTL of biomass in the presence of such catalysts, which are commonly used in catalytic processes in the petrochemical and refining industries, is vast. However, none of the catalysts could generate a compatible bio-oil with conventional liquid transportation fuels because the chemistry in the field of biomass stands in great contrast with the field of petrochemistry, where it deals with petrochemical hydrocarbons. The main problem with the HTL process is that a sequence of successive reactions (a cascade reaction) is involved in transforming raw biomass and biomass-derived platform molecules into value-added chemicals and biofuels. Thus, systems with multiple catalyst materials or catalysis by multifunctional materials are required in the sequence of reactions. For the first time, the thesis provides fundamental insight with respect to the multifunctional catalytic HTL method and offers composite materials as an alternative to conventional heterogeneous catalysts. Advancements made in composite materials were explored in detail, and key factors that influence the activity and stability of each type of composites were highlighted. The effects of advanced modification techniques on the specific surface area, pore size, pore geometry, pore connection, functional group, crystalline structure, and dimension were discussed. Two state-of-the-art heterogeneous catalysts composed of zeolite/hydrochar and graphene/polyurethane were developed for the HTL of macroalgae to gasoline fraction hydrocarbons and valuable chemicals. The results show that the hierarchically structured porosity of composites facilitates the accommodation of macromolecules and their meso and micro derivatives inside the composite and improves the accessibility to Lewis and Bronsted acid sites. The higher heavy gasoline selectivity, lower amount of amino, and aliphatic acids demonstrate that the HTL in the presence of our newly developed composites can be a potential one-pot method for the conversion of biomass to high-quality liquid products. And finally, a biocarbon-based Asymmetric Supercapacitor (ACS) was fabricated within the circular economy concept by integrating pyrolysis and hydrothermal processes.