Microplastics (MPs), defined as plastic pieces <5 mm, pose a growing ecological threat. Various waste management practices, including landfill mining, are implemented globally to address the growing waste problem. The process involves segregating waste into various fractions, among which landfill-mined soil-like material (LMSLM) is utilised for various geotechnical applications. These materials are known to contain various contaminants, including trace metals, organic pollutants, pathogens, and salts. However, the presence of MPs remains poorly documented. This research investigates the occurrence of MPs in mined material recovered through landfill mining activities from MSW dumpsites in India. It characterises their physical and chemical properties, and a field study was conducted to assess MPs’ migration from LMSLM into underlying soil and groundwater. Results revealed varying MPs concentrations ranging from 25,950 to 41,110 items/kg. Most of the particles were fibres and fragments, with 60% measuring less than 425 μm in size. White, transparent, and black were the dominating colours, while PE and PP were the main detected polymers. SEM-EDX analysis affirms the influence of weathering on the MP surface. Results from the field study revealed high MP concentrations of 7400 items/kg at LMSLM/underlying soil interface, which decreases with depth, reaching up to 1100 items/kg in the saturated zone. This suggests continuous MP migration from LMSLM into the unsaturated soil to the groundwater. These results highlight the requirement for protective measures to prevent MP contamination when utilising LMSLM in geotechnical applications.