Based on detailed x-ray diffraction and transmission electron microscopy we have found body-centered-cubic (bcc) Ni upon room-temperature rolling of nanocrystalline (nc) face-centered-cubic (fcc) Ni. The bcc phase forms via the Kurdjumov–Sachs (KS) martensitic transformation mechanism when the von Mises equivalent strain exceeds ∼0.3, much higher than accessible in tensile testing. The fcc and bcc phases keep either the KS or the Nishiyama–Wasserman orientation relationship. Our results provide insights into the deformation physics in nc Ni, namely, the fcc-to-bcc phase transformation can also accommodate plasticity at large plastic strains.