Landslide- or glacier-dammed lakes and associated catastrophic outburst floods represent key geomorphological agents in shaping fluvial landscapes in high-altitude, steep mountain environments. Previous studies have reported hundreds of Late Pleistocene moraine/glacier and landslide dams caused by glacier advances or seismic activity across the southeastern Tibetan Plateau, and confirmed that these dammed lakes significantly impeded river incision into the plateau interior. However, comprehensive exploration for geomorphological and sedimentological records documenting the complete evolutionary cycles of such dammed lakes remains scarce. This study identifies a well-preserved lacustrine-fan delta sedimentary succession associated with the Xiaqu dammed lake in the Yigong Tsangpo basin. Through integrated field observations, sedimentological analyses and chronological data obtained through optical stimulated luminescence (OSL) and AMS radiocarbon dating techniques, we reconstruct the full evolutionary history of the lake, which underwent five distinct evolutionary stages, including initial formation, abrupt failure, secular stability, sedimentary infilling and fluvial incision. The initial landslide dam created at a height of 2,650 m above sea level (a.s.l.) may experience rapid breaching when lake water overtopped the crest, triggering outburst flood event(s). Continuous lacustrine sediments deposited between 4.74 ka and 3.11 ka imply a relative stability period for the remnant dammed lake. Subsequent fluvial deposits, unconformably overlying lacustrine sediments post-siltation, are dated to slightly later than 1.48 ka cal. BP. Furthermore, compiled climate proxy indicators and paleo-landslide inventories at the margins of the Tibetan Plateau provide insights into the roles of extreme events and climate change in the evolution of fluvial landscapes within a regional context.