A study was carried out of a Heusler alloy based on Ni-Mn-In of nonstoichiometric composition, in which magnetic and structural phase transitions occur in the region of room temperature. The effect of severe plastic deformation at low temperatures on the microcrystalline structure, the fracture mode, and the microhardness of the Heusler alloy Ni47Mn42In11 has been investigated. The annealed alloy was subjected to high pressure torsion deformation. Plastic deformation was carried out in Bridgman anvils under a pressure of 8 GPa at a temperature of 77 K. Shear under pressure was performed with the rotation of the lower anvil at a speed of w = 0.3 rpm, the angle of rotation φ was varied from 0 to 5 rpm. The structure of the alloy after deformation was studied by methods of optical and electron microscopy. With the help of scanning electron microscopy, the features of the fracture surface were revealed in the initial state and after deformation effects of various intensities. The structure of the annealed alloy at room temperature is polycrystalline two-phase, consisting of a high-temperature L 21-phase and martensitic crystals, the average grain size is up to 500 μm; upon destruction of this structure, a brittle fracture is observed. It was shown that after deformation by torsion under pressure at liquid nitrogen temperature, the polycrystalline structure of the alloy is refined to a nanocrystalline state with a grain size of up to ≈ 90 nm in the entire volume of the sample, with the destruction of the material acquiring mainly as viscous and improving the plastic properties of the material. Deformation at cryogenic temperature causes a significant increase in microhardness, the alloy is practically doubled in comparison with the initial annealed state, and the martensitic transformation is suppressed.