Non-engineered landfills or open dumpsites are the most common solid waste disposal facilities in developing countries. The absence of proper liner systems in these non-engineered landfills causes deterioration of the nearby surface and sub-surface water resources via leachate migration beneath and around the landfill site. Therefore, it is necessary to understand the contaminant transport mechanisms to predict the long-term impact of a landfill in the subsurface groundwater system for the development of possible remedial measures. The present research aims to simulate the subsurface transport of two heavy metals (Lead and Cadmium) from a non-engineered landfill situated at Boragaon, Guwahati, in North-East India, to the nearby eco-sensitive wetland, Deepor Beel (Ramsar site no. 1207). Based on the hydrogeological information collected from the central groundwater board (CGWB) and field investigation, a single-layer conceptual model of the study area was constructed using Groundwater Modeling Systems (GMS) software. Input parameters for the contaminant transport model were determined from laboratory batch and column experiments with the soil samples collected near the vicinity of the landfill. Numerical simulation of groundwater flow and advective–dispersive transport was then performed using MODFLOW and MT3DMS codes to understand the migration pathway and spatiotemporal variation of heavy metals concentration. The simulation results produced different size plumes of heavy metal contaminated groundwater, which are predominantly expanded in the longitudinal direction, indicating advection-dominated transport mechanism. Particle-tracking simulations further revealed that travel times for the plumes of Lead (Pb)and Cadmium (Cd) to reach the wetland were about 22 and 16 years, respectively. The trend of contour lines shows that, after reaching the wetland, the concentration of heavy metals will be enough to degrade its water quality within a few years. The results obtained from the current simulation study can be used for designing and installing engineered barriers to mitigate the migration of heavy metals into the wetland.