Peatlands contribute ∼20% of dissolved organic carbon (DOC) exported from land to sea. However, potential changes in DOC release from waterlogged peatlands under warming remain poorly understood. Here we conduct an in situ warming experiment in the waterlogged high-altitude peatlands (Zoige), integrating five years of field manipulations with monthly/quarterly porewater monitoring by >100 ¹⁴C measurements, organic matter molecular characterization, and microbial community profiling. We show that warming generally increases peatland porewater DOC concentrations, albeit via different mechanisms under contrasting hydrological regimes. In drained peatlands, increased DOC, characterized by modern carbon with high aromaticity, is linked to elevated plant inputs under warming. Conversely, in waterlogged peatlands, warming releases aged (∼890 years before present; 95% credible interval: 283–1935 years), lipid-rich DOC through enhanced iron reduction by increased iron-reducing bacteria. Our findings highlight that warming destabilizes aged carbon via enhanced iron reduction from waterlogged alpine peatlands—a previously overlooked aquatic pathway generating positive climate feedback in these globally significant ecosystems.