Peatlands are thought to have contributed significantly to the deglacial increase in atmospheric methane concentrations. This connection has previously been made through the examination of the frequency and timing of peat basal dates. However, drawing direct connections between past peatland extent and methane emissions remains somewhat speculative because of missing qualitative and quantitative links between extent, type, hydrology, and emissions of peatlands. Here we use existing records of peat accumulation, peatland expansion, humification, and peatland characterization using lithology and plant macrofossils to quantify methane emissions from past peatlands. Because methane emissions vary by one order of magnitude among different peatland types, this analysis takes into account peatland vegetation composition based on plant macrofossils, regional differences in timing of the fen-to-bog transition, peat accumulation rates, past permafrost extent, and estimations of past relative fen versus bog area to quantify past methane emissions from peatlands. We find that methane emissions from northern high latitude peatlands were 2-11 times higher than previous estimates, and can explain ~70 percent of the northern high latitude source in atmospheric methane concentrations during the Younger Dryas - Preboreal transition, with emissions from thermokarst lakes explaining much of the remaining gradient. The mid-Holocene decline in atmospheric methane concentrations can partially be explained by a slowdown of peatland expansion rates under a cooler climate and the aggradation of permafrost in many peatland regions following the Holocene thermal maximum. Late Holocene increases in atmospheric methane concentrations may be explained by thermokarst development as a result of recent warming.