Darwin Harbour is a macro-tidal estuary in the wet-dry tropics of Australia that supports a significant and intact mangrove ecosystem. Mangrove vegetation surveys suggest the forests are relative stable in terms of area occupied and floristic composition, yet these mangroves occur in the intertidal zone from below mean-sea level through to the highest astronomic tide and are exposed to rates of sea-level rise of 10.8 mm y-1 over the last decade, four-fold higher than the global average. To assess the potential vulnerability to this rapid sea-level rise, surface elevation change was monitored biannually between 2014 and 2025 via 42 surface elevation tables (RSET-MHs) distributed across the 20, 440 ha Darwin Harbour mangrove estate. Elevation trends varied with tidal position and geomorphic setting: seaward zones showed higher surface elevation gains driven by sediment accretion, while landward zones gained elevation primarily through below-ground processes. Position within the Harbour had an influence on surface elevation with riverine settings accumulating more sediment than harbour mangroves. This long-term surface record captures the influences of disturbance events, including a category 2 tropical cyclone, severe convective storms resulting in localised dieback, as well as interannual variations in mean sea level. These results suggest that, despite limited sediment inputs, Darwin Harbour’s mangroves gain some stability from the large tidal range to which they are exposed; however, the seaward fringes remain most at risk, as recovery below mean sea level approaches a critical threshold.