Along the coastal belt of the Ganges-Brahmaputra Delta, the sea level rise is one of a major threat, linked to climate change, affecting millions of people living in Bangladesh and Indian West Bengal. A comprehensive understanding of sea level variability in this region is therefore crucial and should help to anticipate the impacts of climate change and implement adaptation strategies. For the first time, by combining a unique large set of water level measurements, provided by Bangladesh Water Development Board, we reconstruct the 'Regional' relative sea level (RSL) changes since 1970s. For the last four decades, we analyze, through 6 different regions, the trends and decadal/multi-decadal sea level dynamics. We show that the RSL along the delta's coast increased since 1970s at the same pace ( 2.5 mm/yr), or even slightly faster, as the global absolute mean sea level over the same period (1.8 to 2.2 mm/yr). We highlight the importance and the consequences of the RSL interannual variability, mainly linked to ENSO and Indian Ocean Dipole events. Moreover, we able to evaluate, for the first time, 'Regional' land vertical motion trends over the two last decades by using satellite altimetry measurements and 'Regional' RSL reconstructions. We observe subsidence rates through the regions between 1-4 mm/yr over 1993-2012; however, they vary widely according to spatial and time scale considered.