Consul in 146 BC, Mummius was appointed to take command of the Achaean War, and having obtained an easy victory over the incapable Diaeus, entered Corinth after a victory over the defending forces. All the men of Corinth were put to the sword, the women and children were sold into slavery, and the statues, paintings and works of art were seized and shipped to Rome, and then the place was reduced to ashes. However, at least two ancient authors give accounts that suggest Corinth was not completely destroyed (Cicero in Tusc. 3.53, and Dio Cassius 21). The apparently needless cruelty of Mummius in Corinth, by no means characteristic of him, is explained by Mommsen as due to the instructions of the senate, prompted by the mercantile party, which was eager to get rid of a dangerous commercial rival. According to Polybius, his inability to resist the pressure of those around him was responsible for it.
In the subsequent settlement of affairs, Mummius exhibited considerable administrative powers and a high degree of justice and integrity, which gained him the respect of the inhabitants. He especially abstained from offending their religious susceptibilities. On his return to Rome he was honoured with a triumph. In 142 he was censor with Scipio Aemilianus Africanus, whose severity frequently brought him into collision with his more lenient colleague.
Mummius was the first novus homo of plebeian origin to receive an agnomen for military services. His indifference to works of art and ignorance of their value is shown by his well-known remark to those who contracted for the shipment of the treasures of Corinth to Rome, that "if they lost or damaged them, they would have to replace them." For the theatrical pageants exhibited by him he erected a theatre with improved acoustical conditions and seats after the Greek model, thus marking a distinct advance in the construction of places of entertainment.