Vice-proconsul was the title given to an official in the Romulan Senate directly below a proconsul, who in turn was below the praetor.
In the late 2360s, M'ret was a vice-proconsul. In 2369, M'ret spoke out against the repressive policies of the Romulan government and was in danger of being arrested, so Ambassador Spock and the Romulan underground movement arranged for him and two aides to defect to the Federation. (TNG: "Face Of The Enemy")