Vice-Proconsul is the common title given to the official in the Romulan Senate directly below the Proconsul, who in turn is below the Praetor.
In the late 2360s, M'ret was the Vice-Proconsul. In 2368, M'ret spoke out against the repressive policies of the Romulan government and was in danger of being arrested, so Ambassador Spock and the dissident movement arranged for him and two aides to defect to the Federation. (TNG: "Face of the Enemy")