<p>An ideal waveguide display for augmented reality would feature a single-layer waveguide substrate combined with dispersion-free couplers. While metasurfaces have been explored as a potential solution for waveguide displays, severe limitations—such as low efficiency, poor uniformity and chromatic aberration—remain unresolved. Here we introduce a single-layer waveguide display using achromatic metagratings. The proposed metagratings comprise periodic arrays of rectangular nanostructures, diffracting red, green and blue lights in the same direction. Therefore, they ensure an achromatic propagation angle within the single waveguide substrate maintaining high-quality projected images. As a proof of concept, we demonstrate a full-colour augmented reality waveguide display with a 500-μm-thick single-layer waveguide substrate that substantially reduces the device form factor and weight while enhancing brightness and colour uniformity with a sufficient eyebox. This approach overcomes the limitations of traditional augmented reality near-eye optical designs, which rely on multi-layer grating couplers that require complex fabrication processes and are too heavy for ergonomic head-mounted applications.</p>