Eorpwald was the son of Rædwald by a wife whose name is not recorded. He had at least one brother, Rægenhere, and another sibling, Sigeberht, may also have been his brother. Rædwald used the letters R and E when naming two of his own sons (as did his own father when he and his younger brother Eni were named), which suggests that Eorpwald was the younger sibling and would only have become Rædwald's heir after his elder brother Rægenhere was slain in battle in 616.