Conventional high strength alloys lack ductility due to lower work hardening and early onset of damage nucleation. To overcome this deficiency, high entropy alloys (HEAs) enjoy the benefit of metastability of phases to tune the deformation mechanisms for engineering strength and ductility. Inspired by this, here we present friction stir processed Fe40Mn20Co20Cr15Si5 HEA with ultrafine face centered cubic (f.c.c.) γ grains embedded in a refined hexagonal closed packed (h.c.p) ε matrix. Transformation of γ grains and twinning in ε matrix triggered uniform strain partitioning among these phases and sustained work hardening during deformation thereby reversing the conventional strength-ductility trade-off. © 2018 Elsevier Ltd.