She was first said by some to be the natural daughter of Julius Caesar, her mother's lover at the time of her birth. Later on it was said that Servilia offered her up to Caesar when his interest in her mother began to wane - although the former rumour, that his interest in her was paternal, seems the more likely to be true (as it is unlikely that both were true at once: incest not being a vice that Caesar was ever accused of even by his worst enemies). Either could have been the reason for Cicero to remark, at an auction where Caesar had sold goods to Servilia at reduced prices, that they had been discounted by a third (tertia).
Like her mother, Tertia was allowed to outlive her husband Cassius, unmolested by the triumvirs and Augustus. She survived to an advanced age, dying in 22 AD, 64 years after the battle at Philippi, during the reign of the emperor Tiberius. She had amassed a great estate in her long widowhood, and left her fortune to many prominent Romans, although excluded the emperor, which was met with criticism. Tiberius forgave the omission and still allowed a large funeral to be held in her honor, though the masks of Brutus and Cassius were to not be displayed in the procession.