We present a theoretical description of an effect that we call three-photon electro-optical rotation. We consider a high-intensity beam of polarized monochromatic light, which interacts with an assembly of identical molecules. We calculate the probability of the absorption of two photons from this beam of light and the simultaneous reemission of a third photon, which has the same direction of propagation as the incident light and a direction of polarization that is perpendicular to the incident light. The energy of the emitted photon is the sum of the energies of the absorbed photons. We found that the effect is observable in the presence of a homogeneous electric field F, directed along the direction of polarization of the emitted beam of light. The effect is proportional to F and to the molecular dipole moment and it is inversely proportional to the absolute temperature T.