In the tribunate, he served with colleagues including Gnaeus Domitius Ahenobarbus. In the office, Longinus passed a law stripping persons who had their imperium revoked by the Assembly of their seats in the Senate, which was targeted towards the much-hated general Quintus Servilius Caepio who had lost the Battle of Arausio in 107 BC, and afterwards, was then stripped of his proconsular imperium by the Assembly.