Land-ice flow in Antarctica has experienced multi-annual acceleration in response to increased rates of ice thinning, ice-shelf collapse and grounding-line retreat. Superimposed upon this trend, recent observations have revealed that land-ice flow in the Antarctic Peninsula exhibits seasonal velocity variability, with distinct summertime speed-ups. The mechanism, or mechanisms, responsible for driving this seasonality are unconstrained at present, yet detailed, process-based understanding of such forcing will be important for estimating accurately Antarctica’s future contributions to sea level. Here, we perform time-series analysis on an array of remotely-sensed, modelled and reanalysis datasets to examine the influence of potential drivers of ice-flow seasonality in the Antarctic Peninsula. We show that both meltwater presence and ocean temperature act as statistically significant precursors to summertime ice-flow acceleration, although each elicit an ice-velocity response after a distinct lag, with the former prompting a more immediate response. Furthermore, we find that the timing and magnitude of these local drivers are influenced by large-scale climate phenomena, namely the Amundsen Sea Low and the El Niño Southern Oscillation, with the latter initiating an anomalous wintertime ice-flow acceleration event in 2016. This hitherto unidentified link between seasonal ice flow and large-scale climatic forcing may have important implications for ice discharge at and beyond the Antarctic Peninsula in the future, depending upon how the magnitude, frequency and duration of such climate phenomena evolve in a warming world.