We report on the first observation of the diffuse cosmic neutrino flux with the Baikal-GVD neutrino telescope. Using cascadelike events collected by Baikal-GVD in 2018–2021, a significant excess of events over the expected atmospheric background is observed. This excess is consistent with the high-energy diffuse cosmic neutrino flux observed by IceCube. The null cosmic flux assumption is rejected with a significance of 3.05σ. Assuming a single power law model of the astrophysical neutrino flux with identical contribution from each neutrino flavor, the following best-fit parameter values are found: the spectral index γastro=2.58−0.33+0.27 and the flux normalization ϕastro=3.04−1.21+1.52 per one flavor at 100 TeV.Received 25 November 2022Accepted 10 January 2023DOI:https://doi.org/10.1103/PhysRevD.107.042005© 2023 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasNuclear astrophysicsNuclear Physics