This paper presents a novel protection and fault location combined algorithm for mixed overhead transmission lines (OHLs) and underground cables (UGCs). The method is based on applying the Morphological Gradient (MG) to the modal component of synchronized measured currents at both ends of the mixed line to detect the transient components generated by the fault. The proposed method utilizes the sign of superimposed components for discriminating internal and external faults and the difference between the times related to these transient components to detect fault location. The method has been evaluated through various simulations, whereas it has a very low computational burden, it is suitable for online applications. Results have shown high performance of the method against different fault inception angles (FIA), fault resistances, fault types, fault locations, combinations of OHL‐UGC, and even current transformer saturation, noise presence, long cable section, and different sheath‐ground connections.