<p>Self-assembled metal nanoparticles exsolved from host oxides have gained prominence in catalysis and electrochemistry owing to their exceptional activity and stability. Understanding the relation between dopant transport and exsolution is important, as the transport mechanism of dopants toward the surface of the host oxide directly influences exsolution sites, density, and dispersion, ultimately determining catalytic functionality. However, the pathways for dopant transport and their interactions with internal defects during exsolution remain unclear due to the complexity of defects hidden in the bulk. Here, we reveal the exsolution pathway mediated by dislocation evolution within a host oxide perovskite. By employing in situ Bragg coherent X-ray diffraction imaging and transmission electron microscopy, we show that dislocations nucleate in the bulk interior and propagate to the surface during the reduction of Ru-doped BaCe_0.85Y_0.1Ru_0.05O_3-δ. Moreover, we verify that the Ru dopant is specifically correlated with the formation of mixed dislocations, which act as mobile vehicles that dynamically carry Ru defects to the surface in tandem with dislocation propagation. These findings advance our understanding of dislocation dynamics and support the development of exsolved metal nanoparticles for next-generation catalysts.</p>