The design of efficient, robust catalytic materials for the anodic evolution of oxygen in proton exchange membrane water electrolysers remains a great challenge to be overcome for the commercialisation of this promising hydrogen generating technology. In the present work, we demonstrate a simple, one-step organometallic chemical deposition (OMCD) of IrO2 nanoparticles onto Sb-doped SnO2 (ATO) high-surface area support. The resulting IrO2/ATO electrocatalyst was characterised using high-resolution scanning transmission electron microscopy (HR-STEM) and X-ray photoelectron spectroscopy (XPS) to develop an understanding towards the structural and chemical properties of the prepared materials. The OMCD method produced crystalline IrO2 nanoparticles of 2.3 ± 0.7 nm that were uniformly dispersed over the ATO support surface. Most interestingly, structural metal-support interactions were observed in the form of epitaxial anchoring of IrO2 nanoparticles on the ATO support. These characteristics yielded outstanding oxygen evolution performance: a 7-fold increase in Ir mass-specific activity was observed compared to an IrO2-TiO2 commercial benchmark, in combination with excellent stability of our crystalline IrO2.