We present an inversion method that uses self-potential data to invert for the redox potentials of contaminant plumes. A two-layered electrical conductivity structure, in which the boundary corresponds to the water table, is considered. Furthermore, the electrical-dipole sources are assumed to be vertical and located at the water table. The inverse method is applied to surface self-potential measurements made in the vicinity of the Entressen landfill (southern France). The estimated redox potentials correlate well with in situ measurements and their amplitudes are retrieved satisfactorily. This is the first method (to our knowledge) that can be used to estimate the redox potential of contaminant plumes non-invasively and remotely without any in situ measurements.