Peat landslides represent a notable natural hazard that is difficult to assess across complex blanket bog terrain. To aid the assessment of peat landslide susceptibility, we propose a new metric, the range of vertical surface motion (RVSM), quantified from time series data of surface motion measured using interferometric synthetic aperture radar (InSAR). Our expectation is that areas that are more susceptible to landslide will display a high RVSM that is indicative of high amplitude swelling and shrinking of the peat in response to changes in the volume of water stored in the peat over time. To test our hypothesis we examined the spatial distribution of high RVSM values that preceded three peat landslides in Ireland in 2020 and over a large area of blanket bog. We observed that high RVSM was closely associated with the known failures and with inferred points of initial failure, and that the areas of high RVSM were detectable up to two years in advance of failure. In the blanket bog landscape, high RVSM was associated with areas where landscape hydrology would favour thick peat and subsequent potential instability. We conclude that RVSM mapping has potential for refining national-scale assessments of peat landslide susceptibility.