The 8.2 ka event, the most abrupt climatic anomaly of the Holocene, disrupted global climate by weakening the Atlantic Meridional Overturning Circulation (AMOC) due to meltwater influx, triggering widespread climatic and environmental changes. While its impacts are well-documented in and around the North Atlantic, responses in Southeast Asia remain uncertain due to sea level fluctuations and limitations in existing paleoclimate data. This study presents a new multi-proxy analysis of a sediment core from the Kuan Kreng peat swamp forest in southern Thailand. Lithostratigraphy and geochemical analyses (total organic carbon and biomarkers) reveal environmental shifts between coastal lagoon and peat swamp ecosystems primarily driven by early- to mid-Holocene sea level changes. Our record delineates two distinct transitions: (1) from a marine-influenced lagoon to the onset of a peat swamp (8025 ± 20 yr BP) and (2) a subsequent return to lagoon conditions. Evidence based on n-Fatty Acid Methyl Ester (n-FAMEs) suggests that sea level regression due to the 8.2 ka event may have begun before the transition from lagoon to peatland indicated by lithostratigraphy. Branched-glycerol dialkyl glycerol tetraethers (brGDGTs) also indicate environmental changes and possibly cooler temperatures around 8.0 ka BP. Comparisons with published records from the Thai-Malay Peninsula refine the understanding of regional environmental changes, suggesting that the 8.2 ka event likely triggered a temporary regression at the study site, with variations in the monsoon intensity and ITCZ shifts playing a key role in hydroclimate changes.