The coming century is predicted to feature enhanced climatic variability, including increased frequency, intensity, and duration of extreme climatic events. Ecologists are faced with the critical challenge of anticipating potentially nonlinear ecosystem responses to these changes. High-resolution paleoecological data sets that capture past ecosystem responses to climate variability provide valuable long-term perspectives on the sensitivity of ecosystems to climate-forced state shifts. We used a suite of paleoecological analyses at Titus Bog in northwestern Pennsylvania, USA, to test the hypothesis that the development and expansion of floating peatlands in kettlehole basins represents a threshold response to hydroclimate variability. In contrast with expectations of gradual autogenic peat mat expansion, our results indicate that peat mat expansion at Titus Bog was highly episodic and occurred in three distinct pulses centered on 800, 650, and 400 cal yr BP. Each of these expansion events coincided with or immediately followed decadal-to-mutlidecadal droughts recorded in regional paleoclimate reconstructions. These patterns indicate that peatland development in kettlehole basins can follow nonlinear trajectories, with episodes of rapid advancement triggered by climatic forcing. Future climate changes may increase the likelihood of peatland expansion in kettlehole basins, potentially leading to abrupt changes in adjacent lake ecosystems.