The hot workability of intermetallic titanium aluminide alloys can be limited by ductile failure. Titanium aluminides undergo microstructural changes during hot deformation processes, including flow instabilities such as shear bands, flow localization, void formation and growth. In this work, the ductile damage behaviour of a gamma titanium aluminide alloy with a nominal composition of Ti-43.5Al-4Nb-1Mo-0.1B (in at. %) termed TNM, was studied by means of damage modelling implemented in finite element method simulations. The flow localization or α parameter was calculated based on flow softening due to flow instabilities in the material. Predictions by the α instability criteria were compared with traditional models such as Cockcroft & Latham, normalized Cockcroft & Latham, Brozzo and Ayada. Predictions of these instability and damage parameters were validated by hot compression experiments carried out on a Gleeble®3800 simulator. Hot deformation experiments of the TNM alloy were conducted in a wide range of temperatures and strain rates up to a strain of 0.9. Metallography was carried out on deformed specimens using light optical microscopy and scanning electron microscopy to determine damage and flow localization. Deformation at high strain rates was characterized by instabilities due to adiabatic flow such as shear bands and cracks.