The production of biogas (methane) by anaerobic digestion is an important facet to renewable energy, but is subject to instability due to the sensitivity of strictly anaerobic methanogenic archaea (methanogens) to environmental perturbations, such as oxygen. An understanding of the oxidant-sensing mechanisms used by methanogens may lead to the development of more oxidant tolerant (i.e. stable) methanogen strains. MsvR is a redox-sensitive transcriptional regulator that is found exclusively in methanogens. We show here that oxidation of MsvR from Methanosarcina acetivorans (MaMsvR) with hydrogen peroxide oxidizes cysteine thiols, which inactivates MaMsvR binding to its own promoter (PmsvR). Incubation of oxidized MaMsvR with the M. acetivorans thioredoxin system (NADPH, MaTrxR, and MaTrx7) results in reduction of the cysteines back to thiols and activation of PmsvR binding. These data confirm that cysteines are critical for the thiol-disulfide regulation of PmsvR binding by MaMsvR and support a role for the M. acetivorans thioredoxin system in the in vivo activation of MaMsvR. The results support the feasibility of using MaMsvR and PmsvR, along with the Methanosarcina genetic system, to design methanogen strains with oxidant-regulated gene expression systems, which may aid in stabilizing anaerobic digestion.