Its continuous availability as a municipality waste product makes sewage sludge an alternative renewable biofuel in the long term without competing with arable land, as is the case with first-generation biofuels. Pyrolysis liquids of sewage sludge have a high nitrogen and oxygen content that can result in immiscibility with fossil fuels, and thus, need further upgrading. Herein, pyrolysis liquids (feeds and hydrotreated products) were chemically characterised by supercritical fluid chromatography (SFC) with high-resolution mass spectrometry (HRMS) and one and two-dimensional gas chromatography with nitrogen-phosphorous detection (NPD), and HRMS, subsequent feature detection and statistical analysis, to determine the type of compounds that are removed or remain after hydrotreatment at varying processing conditions. Mild hydrotreatment (at comparably low temperatures and residence times) caused only insignificant changes in the chemical composition, whereas, e.g., higher temperatures resulted in lower concentrations of nitrogen, oxygen, and sulphur. Among the chemical species identified were fatty acid amides, fatty acids, quinolines, imidazoles among others. The developed SFC-HRMS and GC-NPD and GC×GC-HRMS methods detailed information on the effects of processing conditions on products of sewage sludge pyrolysis oils.