Synchrotron X-ray laminography was used to reveal the time evolution of the three-dimensional (3D) morphology of micropores in sintered iron during a tensile test. 3D snapshots showed networked open pores growing wider than 20 µm along the tensile direction, resulting in internal necking of the specimen. Finally, these pores initiated cracks perpendicular to the tensile direction by coalescing with surrounding preexisting microvoids or secondary-generated voids immediately before fracture. Topological analysis of the barycentric positions of these microvoids showed that they formed two-dimensional networks within a ~20 µm-radius area. This indicates that microvoid coalescence could occur on shear planes formed close to the enlarged open pores or between closed pores by strain accumulation and play an important role in crack initiation.