Thrasamund was the third son born to Geiseric's fourth son, Gento, and became king in 496 only because all of Geiseric's sons and his own brother, King Gunthamund, all died in their forties. Upon Gunthamund's death, he was one of only two living grandsons of Geiseric, and inherited the throne in accordance with a law enacted by his grandfather bestowing the kingship on the eldest male member of his family.
As king, he has usually been portrayed as an ineffectual ruler. Under his leadership, the Vandal kingdom appears to have continued a decline which began with Geiseric's death, and lost control of nearly all of modern Algeria to the Berber. In the final year of his reign, the important port city of Leptis Magna was sacked by the Berbers, giving further evidence of the Vandals' weakness.
On the other hand, he seems to have maintained a firm grip on the heartland of the Vandal kingdom, which consisted of modern Tunisia and eastern Algeria. He also ended many years of persecution of the Catholics which had begun under his uncle Huneric, a move which improved the Vandals' relations with the Byzantine Empire.
Thrasamund died in 523 and was succeeded by his cousin Hilderic, the firstborn son of Huneric.