Employing Korringa–Kohn–Rostoker Green’s function methodology, our investigation elucidates the previously obscure origins of the anomalous temperature-dependent electrical resistivity behavior of (Ga,Mn)As ferromagnetic semiconductors. Phonon and magnon excitations induced by temperature effects are addressed via the coherent potential approximation, while the Kubo–Greenwood formula is employed to compute transport properties. Consequently, the anomalous temperature-dependent electrical resistivity arising from the ferromagnetic–paramagnetic transition is successfully replicated. Our examination of electronic structures and magnetic interactions reveals pivotal roles played by antisite defects and interstitial Mn atoms in governing this behavior. As this approach enables both the estimation of temperature-dependent transport properties and the assessment of underlying mechanisms from a microscopic standpoint, it holds significant potential as a versatile tool across diverse fields.