Soils across permafrost regions are one of the largest terrestrial pools of mercury (Hg) in the world, storing an estimated 500–1500 Gg of Hg in the top three meters of soil. Ongoing climate-driven thaw threatens to release this legacy Hg into the environment. Efforts to quantify and model this pool have been hindered by a lack of harmonized, spatially resolved observations. To address this, we compiled a database of 117,802 Hg observations collected between 1988 and 2022 from 59 studies across Arctic, sub-Arctic, and alpine permafrost regions of the Northern Hemisphere, including North America, northern Europe, Eurasia and the Tibetan Plateau. The database includes Hg concentration measurements in solid materials – such as soil, leaves, roots, and wood – as well as in water samples from soil porewater, lakes, and rivers across the northern hemisphere permafrost domain. The database enables cross-site synthesis, model calibration and evaluation, and environmental assessments by standardizing and harmonizing data from diverse sources. Data standardization included unit conversion, categorization of observations by type, and quality-control procedures to ensure consistency across studies. Analytical uncertainty was preserved where reported in source studies, and quality control indicators – including range and outlier flags – were applied to support data screening and interpretation. Mercury concentrations vary widely across observations, with lake sediment showing the highest median values (70 ng g−1, IQR: 45–116), followed by soil (50 ng g−1, IQR: 32-90), and vegetation (15 ng g−1, IQR: 9–33). Water observations (total Hg) had a median of 2 ng L−1 (IQR: 2–6). Statistically significant differences in Hg concentrations among observation types were observed at both global and regional scales, generally following the pattern: lake sediment > soil > vegetation, although this ordering is sensitive to regional sampling distribution. These patterns, along with spatial and observation-type biases, highlight the need for improved coverage in underrepresented regions such as Eurasia. The database is freely accessible through Zenodo under the concept https://doi.org/10.5281/zenodo.18300989 (all versions; Olson et al., 2026a), to support ongoing research and model development in Arctic and sub-Arctic Hg cycle studies.