Northern temperate and high-latitude wetlands are a major source of the greenhouse gas methane (CH4). Here, we estimate the sensitivity in the strength of this source to the effects of large Icelandic volcanic eruptions such as the Laki eruption of 1783-1784. We applied spatially explicit modeled sulfate aerosol and S deposition fields from a Laki eruption simulation to a climate-sensitive model of CH4 emissions from wetlands. We estimate that the combined influence on climate and S deposition from the Laki eruption halved the output of CH4 from wetlands north of 30°N for the first 12 months following the eruption. The largest short-term component responsible for the CH4 suppression is the aerosol-influenced surface cooling, although the effect of large-scale S deposition on CH4 emissions provides a longer-term suppressive effect on emissions. Together, we estimate this combination of processes to result in an annual suppression of ~20 Tg CH4 in the year of the eruption and two subsequent years. Further, the impact of the eruption on atmospheric CH4 concentration extends beyond the likely duration of suppressed emission. The modeled effect of this large Icelandic eruption is consistent with ice core records of atmospheric CH4 concentrations at the time and is equivalent, in size, to the current estimated suppressive effect of industrially derived S pollution on the global wetland CH4 source.