Per- and polyfluoroalkyl substances (PFAS) are a class of environmental contaminants of high concern due to their negative health effects and widespread presence in the environment. As new regulations on the use and manufacture of legacy PFAS are imposed, alternative replacement PFAS compounds have emerged. Current targeted methods focus on a short list of legacy and emerging PFAS and are therefore not comprehensive enough for measuring the potential PFAS contamination in environmental samples. Non-targeted analyses (NTA) with high-resolution mass spectrometry (HRMS) is a promising technique for the discovery and identification of new PFAS. Here, HRMS was coupled with liquid chromatography and ion mobility separation on the SELECT SERIES™ Cyclic™ IMS QTOF mass spectrometer to improve the number of detected features in a complex environmental sample: landfill leachate. As PFAS may be present at low levels in complex samples, a data independent acquisition was utilized to get as much information as possible in a single injection. Detected peaks were first compared to an internal HRMS PFAS library for identification. Identifications were filtered based on metrics like accurate mass, retention time error, diagnostic fragments and measured collision cross section (CCS). In the sample, several legacy PFAS including perfluoroalkyl sulfonates, perfluoroalkyl carboxylic acids, and fluorotelomer sulfonates were identified. For the discovery of PFAS not in the suspect library, IMS adds an additional advantage as this class of compounds have lower CCS values compared to other compound classes of similar m/z. In this study, filtering peaks based on their observed drift time and m/z revealed polyhalogenated species that were in the leachate sample even at low intensity levels. A series of PFAS previously unreported were tentatively identified in the leachate samples. As authentic standards for new PFAS are difficult to find, the certainty of proposed structures benefit greatly from the data generated with LC-IMS-HRMS.