We constrain lithospheric thickness across northeastern Eurasia using a new thermo-compositional model that jointly interprets seismic tomography and gravity data, including gravity gradients from the GOCE mission. This integrative approach provides a self-consistent threedimensional thermal structure of the lithosphere that incorporates compositional variations within lithospheric keels, yielding robust thickness estimates. The results demonstrate a strong link between lithospheric thickness and tectonic evolution. Archean and Proterozoic terranes such as the Siberian Craton and the eastern Fennoscandian Shield preserve thick keels (>200 km), reflecting early stabilization through melt depletion (and the interactions with mantle plumes and rifting episodes for the Siberian Craton), while the Timan–Pechora block also retains anomalously thick lithosphere, consistent with Paleozoic orogenic reworking and stabilization. The northeastern Barents Sea displays intermediate lithosphere (160 km to 180 km), likely representing a Proterozoic–Paleozoic fragment within the Arctic basement mosaic. In contrast, the Ural Orogen forms a sharp lithospheric boundary between the East European Craton and the thermally modified West Siberian Plate, which was profoundly affected by Mesozoic rifting and plume activity. East of the Verkhoyansk Range, lithospheric thickness decreases to less than 100 km in Phanerozoic terranes such as Chukotka, the Anadyr–Koryak Fold Belt, and Kamchatka, where subduction, terrane accretion, and arc magmatism maintain a hot, dynamic lithosphere. Overall, the lithospheric structure of northern Eurasia reflects the interplay of four fundamental processes: Archean craton stabilization, Paleozoic orogenesis, Mesozoic plume–rift modification, and ongoing Pacific subduction. These processes collectively shape the strong lateral contrasts that define the geodynamic framework of Eurasia