In this work, we find that polycrystalline CaCuP thin films with degenerate p-type conductivity and high mobility can be deposited by reactive sputtering. The electrical properties are sensitive to the crystalline quality of the film, which decreases as a function of increasing P content. The optical properties are also sensitive to the crystallinity, with stronger optical absorption recorded in the films of lower crystalline quality. We use density functional theory (DFT) to investigate the defect chemistry of CaCuP, finding the copper vacancy to be extremely low in energy and stable into the valence band maximum, giving rise to degenerate semiconducting behaviour. Charge transport theory is used to model the electrical properties of CaCuP, in reasonable agreement with experimental data, and confirm the trend of improved electrical behaviour with crystal quality. We model the absorption behaviour including phonon-mediated indirect transitions, and find that the experimental absorption coefficient is significantly higher than the theoretical prediction. We calculate the band alignment and TCM figure of merit for CaCuP, and compare these to other p-type transparent conductors.