[en] The electronic structure and magnetism of the Heusler alloy Mn₂NiAl have been studied by first-principles calculations. It is found that the phase transformation from the cubic to the tetragonal structure lowers the total energy, indicating that the martensitic phase is more stable and that a phase transition from austenite to martensite may happen at a lower temperature. Thus, ferromagnetic shape memory effect can be expected to occur in Mn₂NiAl or in alloys of similar composition. Mn₂NiAl is a ferrimagnet in both the austenitic and martensitic phases. The total spin moments are 1.48 and 1.14 μ_B/f.u. for the austenite and martensite, respectively. Because the contribution of Ni to the total moment is small, the total moment is mainly determined by the antiparallel aligned Mn(A) and Mn(B) spin moments.