She was the sister of Æthelburg and Saethryth, who were both abbesses of Faremoutiers Abbey in Brie, and also the sister of Æthelthryth, who married firstly Tonberht, an ealderman of the South Gyrwe in the Fens, and secondly Ecgfrith of Northumbria.
Seaxburh married Eorcenberht of Kent, and was the mother of kings Ecgberht (d.