Ferromagnetic shape memory alloys have received increasing interest and have great potential for actuator and sensor applications, the mobility of the parent-martensite interphase interface in such alloys is determined by its interfacial structure and the migration mechanism; therefore, a thorough understanding of its nature is essential. In the present paper, the parent-martensite interface in a Ni2MnGa alloy is studied in the light of the topological model of martensite transformation crystallography, where the habit plane is envisaged comprising coherent terraces and steps. The coherency strains arising on the terrace plane are accommodated by a network of interfacial dislocations, e.g., twinning dislocations originating in the martensite phase, and disconnections. The topological parameters of these defects, i.e., the Burgers vectors, line directions, and dislocation spacings are quantified via rigorous crystallographic analysis and matrix algorithm based on the Frank-Bilby equation. Consequently, martensite transformation crystallographic features, e.g., the habit plane index and the orientation relationship, in the Ni2MnGa alloy are determined and found to be in good agreement with the results predicted by the well-established phenomenological theory.