Pleistarchus' father King Leonidas perished in 480 BC at the Battle of Thermopylae. For the early part of Pleistarchus's reign, his uncle Cleombrotus acted as regent; after Cleombrotus's death in 479 BC, Pleistarchus's cousin Pausanias was regent.[6]
It is unknown whether Pleistarchus was married. He died without an heir, and was succeeded by Pleistoanax, son of Pausanias.[7]
He had no known surviving relatives after his death, marking the end of his bloodline.