Agatha was born about 1021/1025. There have been many claims and hypotheses about her parentage, but a recent plausible case has been made by John P. Ravilious in _The Scottish Genealogist,_ Quarterly Journal of the Scottish Genealogy Society, that she was a daughter of Mieszko II Lambert, king of Poland, and Richeza de Lorraine, making her a sister of Richeza of Poland, the wife of Béla I, king of Hungary. Ravilious and Michael Anne Guido subsequently published an article in _Foundations,_ the journal of the Foundation for Medieval Genealogy, setting forth further evidence concerning the hypothesised Polish parentage of Agatha, including the derivation of the name Agatha (and of her putative sister Gertruda of Poland) from the names of saints associated with the abbey of Nivelles.

Agatha married Edward Atheling of Wessex, son of Edmund II Ironside, king of England, and his wife Ealdgyth. They had three children of whom only their daughter Margaret would have progeny, marrying Máel Coluim mac Donnchada, Malcolm III Canmore, king of Scots.

After the successful invasion of England by Knud 'den Store' and his succession to Edward's father Edmund II Ironside, Knud had expelled Edward and his brother Edmund, sending them to Olof III 'Skötkonung', king of Sweden, who sent them on to Kiev, where his daughter Ingegerd was the spouse of Grand Duke Jaroslav I Vladimirovitch and the mother-in-law of the exiled András, then prince of Hungary, from a younger branch of the Arpád dynasty, who had claimed the throne when the older line became extinct with the death of King Stephan I. András and his younger brothers Levente and Béla had been exiled from Hungary, fearing for their lives. Béla and Levente fled to Poland, where Béla married Richeza, daughter of Mieszko II Lambert. Some sources indicate that Edward travelled to Hungary in 1046, when the brothers András and Béla returned there from exile.

The argument over whether Edward's wife Agatha was Mieszko II's daughter, rather than (say) a Hungarian noblewoman Edward met in Hungary and married there, may never be fully resolved, but the circumstances and timing of his move appear relevant. If Edward was already married when he moved to Hungary that would seem at least consistent with the argument that Agatha was Mieszko II's daughter, as Edward and Agatha's daughter Margaret was born about 1045.

At some stage in the mid 1050s Edward took his family home to England. In 1057 the brothers András and Béla fell out and Béla rebelled when András had his five-year-old son Salomon crowned as his successor, displacing Béla. It has been argued that András' act may have precipitated Edward's decision to leave: if Agatha had been András' sister-in-law, and aunt of Salomon, his act would have strengthened her bonds and those of her husband Edward to Hungary's future; on the other hand, if Agatha was a sister-in-law to Béla (husband of Richeza of Poland) she and Edward would most likely have been inclined to leave Hungary at the time of Béla's rebellion against his brother.

On the other hand, some sources indicate that when King Edward the Confessor learnt that Edward, son of his half-brother Edmund 'Ironside', was still alive, he recalled him to England in 1056, and named him his heir. This 'pull' motive would tend to negate the force of the 'push' motive related to events in Hungary. However, more damaging to the 'push' argument if true is that, according to some sources, when Edward was summoned to England he was in the custody of Emperor Heinrich III. Heinrich died in October 1056, which would suggest that Edward would have left Hungary in early 1056 at the latest.

Edward died in London in 1057, a few days after his return. Agatha died about 1070.