We report the design and experimental realization of a low-loss dielectric metasurface mirror operating at 1064 nm, the primary wavelength of interferometric gravitational-wave detectors. The mirror consists of a single layer of titanium dioxide nanopillars on a glass substrate, achieving high reflectivity via guided-mode resonance. The fabricated mirror has a peak reflectance of 99.10% with a total optical loss of 0.26%, representing, to our knowledge, the highest reflectance and lowest optical loss experimentally demonstrated in a substrate-supported purely amorphous dielectric metasurface mirror operating in the visible to near-infrared. This single-layer metasurface is projected to reduce coating Brownian noise by a factor of 3-5 relative to conventional dielectric Bragg mirrors at comparable reflectivity, which would improve the performance of precision optical cavities currently limited by this noise. These results indicate the potential of dielectric metasurfaces as a platform for next-generation precision measurement systems.