During his consulship, Publius Cornelius Scipio Nasica Serapio opposed Tiberius Gracchus running for a second consecutive tribuneship. Mucius said that he would allow Gracchus to run since that seemed to be the wishes of the people and he did not want to resort to violence to prevent him from running. Scipio though continued to protest and led the mob that killed Gracchus. Mucius did not condemn Scipio for these actions despite his earlier comments.
He later became Pontifex Maximus in 131 BC after the death of his brother, Publius Licinius Crassus Dives Mucianus. He is the last Pontifex Maximus to have published the Annales Maximi, the list of events of the year.