He was born at Patavium, and belonged to a distinguished and wealthy family. The circumstances under which he came to settle in Rome are unknown. At first he was treated with great consideration by Nero, probably owing to the influence of Seneca, and became consul in 56 and one of the keepers of the Sibylline books. In 57 he supported in the senate the cause of the Cilician envoys, who came to Rome to accuse their late governor, Cossutianus Capito, of extortion.
In 59 Thrasea first openly showed his disgust at the behaviour of Nero and the obsequiousness of the senate by retiring without voting after the emperor's letter justifying the murder of Agrippina had been read. In 62 he prevented the execution of the praetor Antistius, who had written a libel upon the emperor, and persuaded the senate to pass a milder sentence. Nero showed his displeasure by refusing to receive Thrasea when the senate went in a body to offer its congratulations on the birth of a princess. From this time (63) till his death in 66 Thrasea retired into private life and did not enter the senate-house again. But his death had been decided upon. The simplicity of his life and his adherence to Stoic principles were looked upon as a reproach to the frivolity and debaucheries of Nero, who "at last yearned to put Virtue itself to death in the persons of Thrasea and Soranus" (Tacitus). Cossutianus Capito, the son-in-law of Tigellinus, who had never forgiven Thrasea for securing his condemnation, and Eprius Marcellus undertook to conduct the prosecution.
Various charges were brought against him, and the senate, awed by the presence of large bodies of troops, had no alternative but to condemn him to death. When the news was brought to Thrasea at his house, where he was entertaining a number of friends, he retired to his chamber, and had the veins of both his arms opened. The surviving text of Tacitus breaks off at the moment when Thrasea was about to address Demetrius, the Cynic philosopher, with whom he had previously on the fatal day held a conversation on the nature of the soul. Thrasea was the subject of a panegyric by Arulenus Rusticus, one of the tribunes, who had offered to put his veto on the decree of the senate, but Thrasea refused to allow him to throw his life away uselessly. Thrasea's own model of life and conduct was the Stoic senator who had warned of Caesar's ambitions, M. Porcius Cato 'Uticensis', on whom he had written a panegyric. Thrasea was one of Plutarch's chief authorities in his biography of Cato.
See Tacitus, Annals (2d. Furneaux), Xlii. 49, Xiv. 12, 48, xv. 20-22, xvi..21-35, containing a full account of his trial and condemnation, Histories ii. 91, iv. 5; Dio Cassius lxi. 15, lxii. 26; Juvenal, Satire V . 36; WA Schmidt, Geschichte der Denk und Glaubensfreiheit (Berlin, 1847); Merivale, Hist. of the Romans under the Empire, ch. 53; F Hersche, Zwei Characterbilder, on Diogenes of Sinope and Paetus (Lucerne, 1865); monographs by AS Hoitsema (Groningen, 1852); and G Joachim (Lahr, 1858); see also Pauly-Wissowa's Realencyclopädie der classischen Altertumswissenschaft (1900), iv. Pt. I.