Studies of the pre-Cenozoic geologic history of the Tibetan Plateau provide important constraints on the timing and spatial variability of crustal thickening and resulting topographic uplift. Here we present new 1:100,000-scale structural mapping and U-Pb detrital zircon analyses from the Domar fold-thrust belt in the western Qiangtang terrane to constrain the history of crustal thickening in this portion of the Tibetan Plateau. We find that (1) Paleozoic strata of the Domar area were shortened prior to deposition of Permian units; (2) the youngest strata in the area are Late Jurassic to Early Cretaceous in age, rather than middle Cretaceous or Cenozoic, as previously interpreted; and (3) the youngest strata record tectonism synchronous with south-directed thrusting in the Domar fold-thrust belt, with no evidence of significant shortening during the Cenozoic India-Asia collision. Together, our results suggest that the majority of the shortening of this region occurred during the middle Mesozoic. In particular, Late Jurassic to Early Cretaceous formation of the Domar fold-thrust belt likely resulted from underthrusting of the northern Lhasa terrane beneath the southern margin of the Qiangtang terrane during the middle Mesozoic Lhasa-Qiangtang collision along the Bangong-Nujiang suture. These findings add to a growing body of geologic evidence indicating that the Tibetan Plateau had already undergone significant shortening, crustal thickening, and likely rock uplift prior to the India-Asia collision.