He belonged to the optimates, and, as consul, led the opposition to the proposed law of the tribune Aulus Gabinius, by which Pompey was to be entrusted with extraordinary powers for the purpose of conducting the war against the pirates.
Shortly afterwards, when the orders that Pompeius had issued were not carried into execution in Gallia Narbonensis, in consequence, as it was supposed, of the intrigues of Piso, Gabinius proposed to deprive the latter of his consulship, an extreme measure which Pompey's prudence would not allow to be brought forward.
But as the senate could not with any decency refuse to lend their aid in suppressing this corrupt practice, they pretended that the law of Cornelius was so severe that no accusers would come forward, and no judges would condemn a criminal.
They therefore made the consuls bring forward a less stringent law (Lex Atilia Calpurnia), imposing a fine on the offender, with exclusion from the senate and all public offices.
Like the other Roman nobles, he plundered his province, and was defended by Cicero in 63 BC when accused of robbing the Allobroges, and of executing unjustly a Cisalpine Gaul.