The riverine flux of terrigenous dissolved organic matter (tDOM) to the ocean is a significant contributor to the global carbon cycle. In response to anthropogenic drivers such as land-use change the flux is expected to increase, and this may impact both the availability of sunlight in coastal ecosystems, and the seawater carbonate system and coastal CO2 fluxes. Yet despite its biogeochemical and ecological significance, there are few long-term and high-resolution time series of tDOM parameters. Corals incorporate fluorescent tDOM molecules from the chromophoric dissolved organic matter (CDOM) pool in their skeletons, and the resulting luminescence variability in coral skeleton cores has traditionally been used to reconstruct hydroclimate variation. Here, we use two replicate coral cores and concurrent in-situ biogeochemical data from the Sunda Sea Shelf in Southeast Asia, where coastal peatlands supply high tDOM inputs, to show that variability in coral luminescence green-to-blue ratios (coral G/B) can be used to quantitatively reconstruct the concentration of terrigenous dissolved organic carbon (tDOC). Moreover, coral G/B can be used to reconstruct the full absorption spectrum of CDOM from 230–550 nm, as well as the specific ultraviolet absorbance at 254 nm (SUVA254) of the DOM pool. Comparison to a core from Borneo shows that there may be site-specific offsets in the G/B–CDOM absorption relationship, but that the slope of the relationship is very similar, validating the robustness of the proxy. By demonstrating that coral cores can be used to estimate past changes in coastal tDOC and CDOM, we establish a method to study natural and anthropogenic drivers of land–ocean tDOM fluxes and their ecological consequences in tropical coastal seas over decadal to centennial time scales.