The southeastern tropical Indian Ocean (SETIO) is a dynamically active region where water from Pacific ocean flows into the Indian Ocean. Here, surface current variability plays a critical role in the regional ocean dynamics and marine ecosystem functioning. However, surface current variability in this region remains poorly characterised, owing to the lack of high-resolution in situ observations. This study uses Lagrangian surface drifter data to investigate the seasonal variability of surface currents in SETIO, with broader implications for surface current dynamics across the southeastern tropical Indian Ocean. A total of 119 surface drifters were deployed at 123.3°E, 13.8°S between 2019 and 2022 and operated for approximately eight months, providing high temporal (~5min) and spatial (~120m) resolution data within the upper 0.6m of the ocean surface. Seasonal variability was characterised by analysing drifter trajectories that crossed 120°E and propagated eastward. Drifter crossings during April–June occurred at southerly latitudes (~13–16°S), whilst those during July–November were displaced northward (~9–12°S), reflecting a seasonal shift of approximately 4° in the latitudinal position of eastward-flowing surface currents. These findings have direct implications for the transport of buoyant materials (e.g., fish eggs and larvae, oil, and plastics) in the SETIO.