He was born in Paphlagonia and taught at Phasis. Apart from a short sojourn in Rome, he resided in Constantinople during the rest of his life. He was the son of Eugenius, who was also a distinguished philosopher, and who is more than once mentioned in the orations of Themistius. Themistius was instructed by his father in philosophy, and devoted himself chiefly to Aristotle, though he also studied Pythagoreanism and Platonism. While still a youth he wrote commentaries on Aristotle, which were made public without his consent, and obtained for him a high reputation. He passed his youth in Asia Minor and Syria. He first met with Constantius II when the emperor visited Ancyra in Galatia in the eleventh year of his reign, 347, on which occasion Themistius delivered the first of his extant orations, "Peri Philanthropias". It was not long after that he moved to Constantinople, where he taught philosophy for twenty years. In 355 he was made a senator; and the letter is still extant, in which Constantius recommends him to the senate, and speaks in the highest terms both of Themistius himself and of his father. We also possess the oration of thanks which Themistius addressed to the senate of Constantinople early in 356, in reply to the emperor's letter. In 357 he recited in the senate of Constantinople two orations in honour of Constantius, which were intended to have been delivered before the emperor himself, who was then at Rome. As a reward, Constantius conferred upon him the honour of a bronze statue; and, in 361, he was appointed to the praetorian rank by a decree still extant. In 358–359, Themistius may have served as proconsul of Constantinople in 358; he was the last to hold that office, before the position was elevated to the status of urban prefect.