As legate of Julius Caesar's 12th Legion during his Gallic Wars, he was defeated by the Nantuates in 57 BC in the Battle of Octodurus. Later, however, angered due to Caesar's opposition to his campaign for the consulship, he joined the conspiracy with Brutus and Cassius, and was consequently condemned to death by the Pedian law. He was the great grandfather of the Roman Emperor of the same name.