A natural diamond surface was nanopatterned in a subablative scanning mode by multiple tightly focused 515-nm, 300-fs laser pulses, resulting in regular surface metagratings (nanoripples) with a subwavelength period of Λ ∼ 100 nm, an almost undistorted crystalline structure, free from sp2-carbon, oriented perpendicular to the laser polarization, and stackable both along and normal to their stripes. In the visible-near-IR ranges (400–800 nm), these metagratings demonstrate the pronounced resonant antireflective effect in the wavelength range near ∼4Λ, while the overall specular reflectance/transmittance is considerably diminished with respect to both the simulation results and the reference diamond surface, indicating strong (∼50%) coupling/scattering of light inside the crystal. Our modeling indicates the laser wavelength-dependent plasmon-based tunability of metagrating periods, implying the corresponding tunability of their spectral response.