The Cenozoic strata of the Xining Basin, NE Tibet, have provided crucial records for understanding the tectonic and paleo-environmental evolution of the region. Yet, the age for the lower part of the sedimentary stratigraphy and consequently the early tectonic evolution of the basin remain debated. Here, we present the litho- and magnetostratigraphy of various early Eocene sections throughout the Xining Basin and provide two possible age models independently constrained by the radiometric age of a carbonate bed. Our study extends the dated Eocene stratigraphy down to an unconformity at 53.0 Ma, which is coeval with increased uplift of the nearby Western Qinling Shan and the formation of flexural basins in northern Tibet related to the far-field effects of the India-Asia collision. However, the Paleogene Xining Basin lacks the characteristic features of these foreland basins such as high sedimentation rates and coarsening due to foredeep propagation, which appear only later during the Neogene. Instead, the strata show NW-SE extensional features during the Cretaceous. Here, we propose that this regime persisted until the Paleogene, coeval with Eocene grabens developing further east and related to the subduction of the Pacific Plate. Yet, the rotations and unconformities observed in the Xining Basin strata show that the basin was increasingly affected by the growing Tibetan Plateau throughout the Paleogene and Neogene while experiencing a transition from extension to transpression and/or transtension.