As tribune of the people in 131 BC, Carbo carried the lex Papiria extending the secret ballot for the enactment and repeal of laws.
He also proposed that the tribunes should be allowed to become candidates for the same office in successive years, a response to the fate of Tiberius.
The proposal was defeated, having been opposed by Scipio Aemilianus, in whose sudden death in 129 BC Carbo was suspected of having a hand.
[2] Carbo subsequently went over to the anti-populist optimates, and as consul in 120 BC successfully defended Lucius Opimius, when he was impeached for the murder of a citizen (Gaius Gracchus) without a trial.
[2][3] His son, Gaius Papirius Carbo Arvina, was remembered for his attempts to avenge his father's fate.