Ælfwynn was born to Æthelflæd and Æthelred, Lady of the Mercians before her, but her date of birth is not recorded. She was probably born soon after her parents’ marriage, which happened between 882 and 887. It is possible that her mother was unable to have more children after a difficult birth. She first appears in contemporary accounts in 904 on a charter recording the lease of land. Her father died in 911 after which her mother was chosen as Lady of the Mercians.
Her mother was a daughter of Alfred the Great and thus related to the Kings of England. After her mother’s sudden death in June 918, Ælfwynn succeeded her as Lady of the Mercians. However, she lacked the broad support her mother had. Her uncle, King Edward the Elder of England removed her from power, and there was no opposition to this. He decided to send her to Wessex in December 918, but there is no record of her after her removal from power. It is likely that she entered the religious life.
Mercia was absorbed into the Kingdom of the Anglo-Saxons, later the Kingdom of England.