In many Indian cities, a large amount of waste is produced daily due to the growing population. Solid waste is often disposed of in landfills close to the city because there are no organized procedures for managing solid waste. These landfills with all kinds of garbage seriously threaten the environment. To make matters worse, hazardous chemicals and industrial waste are dumped in these landfills. When rainwater percolates through this hazardous material, it becomes leachate and causes groundwater contamination. Leachate is a hazardous liquid and one of the major problems in landfills; it causes serious environmental issues like contaminating underground water and soils. Open dumping and landfills resulted in the accumulation of large amounts of leachate-contaminated soil around. The present study focused on the effects of landfill leachate on black cotton soil (BCS). Leachate was mixed with BCS at different concentrations as 0, 5, 10, 15, and 20% for laboratory investigation. The Geotechnical properties of leachate-contaminated BCS were examined for specific gravity, moisture content, grain size distribution, Atterberg's limit, compaction, hydraulic conductivity, and shear strength. Leachate content raised the soil's liquid limit and plasticity index. The results showed that effective cohesion increases and friction angle decreases due to increased leachate concentration. The present study shows an application for safe landfill design.