In recent years, doped half-Heusler compounds have attracted significant attention due to their tunable electronic, magnetic, and transport properties, making them promising candidates for spintronics applications. In this work, we investigate the effect of magnetic Mn doping on the structural stability, electronic structure, magnetism, and intrinsic anomalous Hall effect of the half-Heusler compound HfPtSi using first-principles density functional theory (DFT) calculations. Phonon dispersion calculations confirm the dynamical stability of both pristine and Mn-doped HfPtSi. The calculated electronic band structure shows that pristine HfPtSi exhibits semiconducting behavior. However, substitution of Mn at the Hf site significantly modifies the electronic structure and induces a ferromagnetic ground state with a magnetic moment of 3 μB per unit cell. As a result, the doped system exhibits half-metallic behavior, where the spin-up channel becomes metallic while the spin-down channel remains insulating. The emergence of ferromagnetism together with strong spin–orbit coupling (SOC) gives rise to a pronounced anomalous Hall effect originating from enhanced Berry curvature near the Fermi level. The calculated anomalous Hall conductivity reaches approximately 200 Ω⁻¹ cm⁻¹ at the Fermi level and increases to about 500 Ω⁻¹ cm⁻¹ at 100 meV above the Fermi level, which is comparable to several reported half-metallic ferromagnets. These results suggest that Mn-doped HfPtSi is a promising candidate for next-generation spintronic devices.