As a supporter of the senatorial party, he opposed the triumvirs, resorting to military force during the Perusine War.
As tribunus plebis in 44 BC, Canutius was violently opposed to Marcus Antonius, one of Caesar's closest allies.
Towards the end of October, Octavianus approached the city of Rome, and Canutius went out to meet him, in order to learn his intentions.
When the latter summoned the senate to the Capitol on November 28, in order to declare Octavianus an enemy of the state, he would not allow Canutius and two of his fellow tribunes, Decimus Carfulenus and Lucius Cassius Longinus, to approach the Capitol, lest they should put their veto upon the decree of the senate.
[2] After the departure of Antonius from Rome to prosecute the war against Decimus Junius Brutus in Cisalpine Gaul, Canutius had full scope for indulging his hostility to Antonius, and constantly attacked him in the most furious manner, continua rabie lacerabat.