The climate change challenge has prompted global governments and international organizations to implement measures aimed at reducing greenhouse gas emissions and mitigating their impact on the ecosystem. The pulp and paper industry, a major contributor to global waste generation, often lacks efficient waste disposal methods despite the energy-rich nature of its waste products. Consequently, there is a pressing need to intensify research efforts on valorizing and utilizing pulp and paper waste residues thereby checking the inordinate disposal of effluents from this sector, hence this thesis. The objective of this research is to investigate the effects of reaction parameters such as temperature, residence time, feed concentration and catalysts on the yield of biocrude from the Hydrothermal Liquefaction (HTL) of pulp and paper mill residues. These reaction parameters were taken through non-catalytic and catalytic optimization. While Central Composite Design (CCD) was used in the design of experiments, Response Surface Methodology (RSM) was utilized in optimization. The optimum parametric conditions obtained are temperature: 340oC, residence Time: 56min and feed concentration: 5%. Zeolite (HZSM-5), gamma-alumina (γ-Al2O3), activated carbon and potassium carbonate (K2CO3) were utilized as catalysts and their performances with respect to biocrude yield improvement were evaluated. The order of catalytic effect on biocrude yield is potassium carbonate (K2CO3) > gamma-alumina (γ-Al2O3) > zeolite (HZSM-5) > activated carbon. However, due to the hygroscopic nature of potassium carbonate it cannot be recovered and re-used. As a result of this deficiency, gamma-alumina was adopted as the best (recyclable) catalyst in this study. Catalyst Characterization, such as N2 Physisorption Analysis (BET), Fourier-Transform InfraRed (FTIR) Spectroscopy, Powder X-ray Diffraction (XRD), Scanning Electron Microscopy / Energy Dispersive X-Ray Spectroscopy (SEM/EDS), and Temperature-Programmed Desorption (TPD). were performed on the fresh and spent catalysts to study their properties and make informed inferences on their impacts on biocrude yield. Finally, an intrinsic kinetic model was developed to derive a rate equation that could be easily integrated with generalized equations for rates of physical transport processes. This integration would enable the development of a reactor model that is capable of extrapolating across a spectrum of reactor operating circumstances. Limitations to mass transport were initially eliminated to establish the kinetic limited region. From the kinetic study, a first-order equation was proposed. The activation energy and pre-exponential factor of the reaction are 15.981 KJ/mol and 0.254 s-1 respectively. The average absolute deviation (3.40%) of the kinetic model showed that the model is an excellent fit for the hydrothermal liquefaction process. Based on the findings from this research, it was concluded that γ-alumina is an appropriate catalyst precursor to efficiently convert pulp and paper mill residues into biocrude, producing the highest biocrude yield of around 26%, which may be attributed to its selectivity, high level of crystallinity, and acidity. Further investigations into hydrothermal liquefaction are recommended, with an emphasis on varying factors such as pressure, feed mass to catalyst ratio, and reactor stirrer speed.