We investigated the athermal irradiation-induced swelling and creep in iron subjecting to the application of external uniaxial stress. We studied this through atomic scale simulations using the creation-relaxation algorithm. We also calculated the defect relaxation volume density tensors (or eigenstrain) as a function of external uniaxial stress. Beyond the dose value corresponding to isolated defects formation, interstitial-type defect clusters form with polarization causing crystal growth in the direction where tensile stress is applied, and growth in the other two perpendicular directions when a compressive stress is applied. The microstructure in terms of the concentrations of vacancies, isolated self-interstitial atoms, Laves phases clusters, and dislocations is not much affected by the external stress, up to at least $\pm$1 GPa. The main cause of the biased crystal growth is due to the anisotropic formation of new crystal planes due to coalescence of interstitial defect clusters. Extra lattice planes form and lead to plastic deformation according to the direction and magnitude of the external stress.