This dataset provides the onset dates of major Northern Hemisphere Sudden Stratospheric Warming (SSW) events, objectively classified into three types: Displacement–Displacement (DD), Displacement–Split (DS), and Split–Split (SS). The classification follows the wave–amplitude–based methodology introduced by Choi et al. (2019), which uses geopotential height at 10 hPa averaged over 55–65°N to determine the dominant planetary–wave structure associated with each event. For each SSW event, the central date is converted to a standard calendar date (Year–Month–Day) and Day of Year (DOY). The NASA MERRA reanalysis is used to identify and classify SSW events for the period 1979–2014. This dataset can be used for studies of stratosphere–troposphere coupling, polar vortex variability, wintertime climate dynamics, and climate-model evaluation. The dataset is associated with the study published in Choi et al. (2019), DOI: 10.1175/JCLI-D-18-0223.1.