<p>The equilibrium and non-equilibrium low-temperature phases of Nb₅₀Ru₅₀ alloy have been investigated using ab initio calculations (thermodynamic, elastic, and electronic properties) in conjunction with experimental microstructural and phase analyses. Low-temperature phases in Nb₅₀Ru₅₀ alloy originate from the transformation of tetragonal L1₀ phase at 750&#xa0;°C, which potentially makes it useful for designing high-temperature shape memory alloys. Current results showed that the monoclinic phase <i>P2m</i> is the most energetically stable under equilibrium conditions, and this is complemented by the absence of negative frequencies in the phonon dispersion curves. However, negative frequencies were observed on the orthorhombic phase <i>Cmmm</i>, indicating that it is a metastable martensite phase. Therefore, two low-temperature phases of Nb₅₀Ru₅₀ have been determined, namely <i>P2m</i> and <i>Cmmm</i>. This forms the basis for further designing of the alloy with superior shape memory properties since <i>P2m</i> is softer and exhibits lower symmetry compared to the brittle L1₀ phase.</p> Graphical abstract <p></p>