We report, an accurate and robust, interatomic pair potential for the technologically important transparent, conducting oxide indium sesquioxide (In2O3). The potential is optimized, for the thermodynamically stable bixbyite phase, and it is then used to explore the relative stability and physical properties of five sesquioxide polymorphs and their high-pressure phase transitions. The potential is further employed to investigate the formation of intrinsic defects at the limit of infinite dilution through the embedded Mott-Littleton approach. The anion Frenkel pair is determined to be the lowest energy source of ionic disorder with an energy of formation of 3.2 eV per defect, which can be explained by the presence of intrinsic anion vacancy sites in the bixbyite structure. In contrast, both the cation Frenkel pair (6.9 eV) and Schottky defect (4.4 eV) are less thermodynamically stable. The Schottky formation energy is less in the high pressure phases; however, it remains above 4 eV at elevated pressures.