This work investigates the use of subcritical water to support the production of biodiesel and renewable diesel from activated sludge derived lipids. The activated sludge slurry was collected from two sewage works in the United Kingdom at different seasons. The biomass content of the slurry was obtained by filtration and dried to a constant weight. The results showed that total biomass content in the activated sludge slurry was dependent on its source and seasons collected. The lipid yields obtained using organic solvents were 2.8 - 7.4 wt. %. The highest yield of FAMEs from acidic methanolysis of lipid extract was 13.9 (wt. %) or 0.4 (wt/wt. %, on dry activated sludge basis), with palmitic acid as the predominant fatty acid. The low yield of the lipid extract increased under subcritical water treatment and optimisation using Design of Experiment (DoE) to 41.0 (wt/wt) %. The lipid extract was further investigated for potential use as a feedstock for renewable diesel production, by catalytic hydrothermal decarboxylation. The maximum yields of the primary hydrocarbon products pentadecane and heptadecane from fatty acids: palmitic, oleic and stearic acids were 23.2% and 15.2%, respectively, obtained after 1 h hydrothermal decarboxylation in the presence of 5% Pt/C.