The Shillong plateau is a unique basement-cored uplift in the foreland of the eastern Himalaya that accommodates part of the India-Eurasia convergence since the late Miocene. It was uplifted in the late Pliocene to 1,600 metres, potentially inducing regional climatic perturbations by orographically condensing part of the Indian Summer Monsoon (ISM) precipitations along its southern flank. As such, the eastern Himalaya-Shillong plateau-ISM is suited to investigate effects of tectonics, climate and erosion in a mountain range-broken foreland system. This study focuses on a 2200 m-thick sedimentary section of the Siwalik Group strategically located in the lee of the Shillong plateau along the Dungsam Chu at the front of the eastern Bhutan Himalaya. We have performed magnetostratigraphy constrained by vitrinite reflectance and detrital apatite fission-track dating, combined with sedimentological and palynological analyses. We show that (1) the section was deposited between ~7 and 1 Ma in a marginal marine deltaic transitioning into continental environment after 5 Ma, (2) depositional environments and paleoclimate were humid with no major change during the depositional period indicating that the orographic effect of the Shillong plateau had an unexpected limited impact on the paleoclimate of the Bhutanese foothills and (3) the diminution of the flexural subsidence in the basin and/or of the detrital input from the range is attributable to a slowdown of the displacement rates along the Main Boundary Thrust in eastern Bhutan during the latest Miocene – Pleistocene, in response to increasing partitioning of the India-Eurasia convergence into the active faults bounding the Shillong plateau.