In time, Tarquin felt ready to seize the throne. He bestowed presents upon them, and spread criticism of Servius the king. Tarquin solicited the support of the patrician senators, especially those from houses that had been raised to senatorial rank under Tarquin the Elder. Tullia encouraged her husband to advance his own position, ultimately persuading him to usurp her father, king Servius.
They had three sons: Titus, Arruns, and Sextus, and a daughter, Tarquinia, who married Octavius Mamilius, the prince of Tusculum. After the murder of their spouses, Tarquin and Tullia were married. She came to despise him, and conspired with Tarquin to bring about the deaths of Tullia Major and Arruns. Her younger sister, Tullia Minor, was of fiercer temperament, but her husband Arruns was not. The elder sister, Tullia Major, was of mild disposition, yet married the ambitious Tarquin. One of Tarquin's sisters, Tarquinia, married Marcus Junius Brutus, and was the mother of Lucius Junius Brutus, one of the men who would later lead the overthrow of the Roman Kingdom. To forestall further dynastic strife, Servius married his daughters, known to history as Tullia Major and Tullia Minor, to Lucius Tarquinius Superbus, the future king, and his brother Arruns. This may recollect an otherwise forgotten attempt by the sons of Tarquin the Elder to reclaim the throne. Īccording to an Etruscan tradition, the hero Macstarna, usually equated with Servius Tullius, defeated and killed a Roman named Gnaeus Tarquinius, and rescued the brothers Caelius and Aulus Vibenna from captivity. When the sons of Marcius subsequently arranged the elder Tarquin's assassination in 579 BC, Tanaquil placed Servius Tullius on the throne, in preference to her own sons or grandsons.
Tanaquil had engineered her husband's succession to the Roman kingdom on the death of Ancus Marcius. The most ancient sources, such as that of Quintus Fabius Pictor, assert Tarquin was the son of Tarquinius Priscus, but modern historians believe that to be "impossible" under the traditional chronology, indicating either he was Priscus' grandson or that the traditional chronology itself is "unsound".