Rising temperatures have led to permafrost degradation throughout the Arctic. The melting of excess ground ice leads to a loss of structural support and consolidation of soils. As a consequence, the surface subsides seasonally when the active layer thaws, or long-term when the active layer deepens. Therefore, inter-annual thaw subsidence is an important metric for monitoring permafrost degradation. With temperature rise reaching twice the Arctic average, warming trends in Svalbard are particularly high, leading to severe impacts on permafrost conditions and periglacial landscapes. However, knowledge on subsurface permafrost changes in Svalbard is mostly limited to a few in-situ observations. In this study, I spatially expanded research on permafrost degradation by applying a two-fold approach to quantify thaw subsidence in the Bayelva basin, northwestern Svalbard. Firstly, I oregistered and differencedhigh-resolution digital elevation models (DEMs) for a period of more than 80 years (1936, 1995, 2008, 2010, 2019, and 2020). Secondly, during a field campaign in summer 2023, I measured Global Navigation Satellite System (GNSS) positions and calculated subsidence rates since a previous GNSS survey in 2019. In addition, I analysed how elevation change relates to landscape, terrain forms, vegetation cover, and timing of snow disappearance. Finally, I compared thaw subsidence in the Bayelva basin to the surrounding Brøgger peninsula. My findings show a clear elevation loss trend in the Bayelva basin that has persisted for decades and stretches across the entire study area. I found that periglacial terrain subsided at rates of −2.6 to −6.4 cm/year in DEM-based and −0.7 cm/year in GNSS-based analyses with larger subsidence during the 20th century than during recent observation periods. Within the periglacial landscape, I observed slightly larger subsidence in topographic depressions and for areas that are longer snow-covered. My study further suggests that the Bayelva basin is a representative subregion of the northern Brøgger peninsula as subsidence rates and patterns are generally similar. In this study, I demonstrated the challenges of thaw subsidence quantification in periglacial areas with a lack of stable reference terrain. At the same time, my results highlight the great potential of multi-temporal DEMs and repeated GNSS measurements for monitoring long-term elevation changes. This study represents a pioneering effort in the area, revealing ongoing subsidence in the Bayelva basin for the first time and indicating widespread ground ice loss, a process notoriously difficult to detect. I conclude that thaw subsidence is a crucial yet often underestimated component of permafrost landscapes in the warming Arctic.