By studying the intrinsic and extrinsic defect chemistry, we were able to identify an effective doping strategy in order to realise degenerate conductivity through Ga-doping. We have used state-of-the-art packages to predict carrier concentrations and to calculate electron scattering rates, giving a more accurate prediction of charge transport properties that goes beyond the constant relaxation time approximation. Overall, we find good qualitative agreement between these predictions and our single crystals, with our best samples achieving carrier concentrations in excess of 2 × 10 20 cm -3 , electron mobility up to 49 cm 2 V -1 s -1 and conductivity of 1890 S cm -1 . The optical behaviour of Ga-doped ZnSb 2 O 6 is also promising, with a direct (forbidden) band gap of around 3.4 eV and optical transmittance greater than 99% at commercially relevant thicknesses. The next logical step is to develop a thin film deposition process for Ga-doped ZnSb 2 O 6 , in order to test its performance when incorporated into a device, and to better understand the relationship between charge carrier concentration, transport properties and optical band gap. Overall, this discovery is a significant milestone in the development of earth-abundant transparent conductors, offering a high-performance, low-cost alternative to industry standard materials with a unique band edge energy alignment, and opens the door to a whole family of Sb(V)-based transparent conducting oxides.