Metal nanowires possess excellent flexibility as well as electrical and thermal properties, offering broad prospects in flexible electronics, energy storage, electrocatalysis, optics, sensing, and so on. Achieving in situ growth of nanowires on metallic matrices improves interfacial bonding and device stability. Nevertheless, effective methods for in situ growth on metal substrates remain limited. In this work, according to the active atom mechanism of metal whisker growth, the layered compound Ti2SnC was implanted into an Al matrix as the Sn atom source. It was found that through a thermal-diffusion route, Sn atoms escape from the Ti2SnC lattice and diffuse to the Al surface, where Sn nanowires with diameters of 200–800 nm are formed. XRD and DSC confirmed the outward diffusion of Sn from Ti2SnC, and the morphological and structural features of the Sn nanowires were characterized by SEM and TEM. Based on these characterization studies, a thermal-diffusion-driven model for nanowire growth from atomized Sn in metallic matrices is proposed. The concept is further validated in an Al/Ti2InC system, suggesting the universality of this approach. This work provides an effective approach for in situ nanowire growth on metallic substrates and offers new insight into diffusion-driven whisker formation in metal/MAX-phase systems.