The purge air from the compressor in the form of bleed air is injected into the mainstream flow to prevent hot air ingestion in the wheel space. This purge flow mixes with the mainstream flow and increases the secondary flow losses by altering the flow structures near the endwall, thus reducing the turbine efficiency. The research aims at incorporating endwall contouring on the blades to improve turbine performance and reduce secondary flow losses. The numerical prediction of the generic high-pressure transonic axial turbine with purge flow passage is considered for the study. The steady-state computational analysis is carried out using Ansys CFX, with SST k-ω as the turbulence model. The endwall fillet radius has been incorporated into the hub and the shroud profiles of the blades. The turbine performance metrics in terms of static entropy, temperature, blade loading, streamlines, and sealing effectiveness are evaluated and compared with a baseline reference configuration without endwall contouring. The endwall fillet reduces the secondary flow losses at the blades’ leading edge and increases the endwall cooling. The blade loading on the rotor blade decreases with the increase in the fillet radius.