The field of transparent ceramics is enjoying a renaissance, as refractory oxides are being developed as alternatives to single crystals in high-performance laser systems. However, a significant challenge remains regarding the reduction of the grain size to sufficiently subwavelength dimensions in order to achieve the same degree of optical transparency as the single-crystal analog. Here we report transparent yttria $\left({\mathrm{Y}}_2{\mathrm{O}}_3\right)$ ceramics that were synthesized by a pressure-assisted, two-step, low-temperature sintering process with an average grain size of $300\mathrm{nm}$ . These nanograined ceramics exhibit equivalent transmission to single crystalline yttria for wavelengths greater than about $1200\mathrm{nm}$ . The single-crystal-like transmittance of the nanograined yttria ceramics in the visible and IR region is an important advancement for the use of these materials in more-extreme environments, including high-energy laser systems where reduction of scattering is paramount.