Subsea permafrost, which is perennially cryotic sediment lying below sea level, forms when rising seas during interglacials flood terrestrial permafrost on the Arctic continental shelf.  Though inaccessibility has limited direct measurements of Arctic submarine permafrost distribution, current estimates suggest that permafrost underlies 2.5 million km² of the Arctic shelf and reaches a thickness of up to over 700 m below the sea floor in parts of the Kara and Laptev seas.Subsea permafrost has received renewed attention in recent years because its thawing may release greenhouse gases from very poorly constrained organic carbon and gas sources.  The distribution of subsea permafrost depends primarily on local sea level variations, with transient air temperature, geothermal heat flux, and ice sheet fluctuations playing secondary roles. Yet to date, no submarine permafrost model has included local sea level that differs from the global mean due to glacial isostatic adjustment (GIA). Here we present the first pan-Arctic model of permafrost development over multiple glacial cycles to incorporate relative sea level forcing that accounts for the gravitational, rotational, and deformational effects of loading a viscoelastic Earth with ice or liquid water mass.  This model allows us to explore the effect that relative sea level has on permafrost development and to produce new estimates for present-day subsea permafrost area, volume, and ice content.  Additionally, we extend the subsea permafrost simulation for the range of selective socioeconomic pathways (SSP) outlined in the International Panel on Climate Change’s sixth assessment report.  This enables us to quantify the millennial-scale sensitivity of subsea permafrost to 21^st century emissions scenarios, explore the role of relative sea level in that sensitivity, and place improved constraints on the vulnerability of Arctic subsea permafrost to climate warming.