She grew up under guidance of her mother, and also of Queen Joan I of Navarre, the wife of her half-brother, King Philip IV.

The death of his beloved first wife, Eleanor of Castile, in 1290, left King Edward I of England grief-stricken.

In summer of 1291, Edward betrothed his son to Blanche, half-sister to Margaret and Philip IV, in order to achieve peace with France.

This in no way lessened her dignity as the king's wife, however, for she used the royal title in her letters and documents, and appeared publicly wearing a crown even though she had not received one during a formal rite of investiture.

[7] Edward soon returned to the Scottish border to continue his campaigns and left Margaret in London, but she had become pregnant quickly after the wedding.

She and her stepson, who was only five years younger than she, also became fond of each other: he once made her a gift of an expensive ruby and gold ring, and she on one occasion rescued many of the prince's friends from the wrath of the king.

He had realised the wife he had gained was "a pearl of great price" as Margaret was respected for her beauty, virtue, and piety.

Margaret was not pleased when Edward II elevated Piers Gaveston to become Earl of Cornwall upon his father's death, since the title had been meant for one of her own sons.

In May 1308, an anonymous informer reported that Margaret had provided £40,000 along with Philip IV to support the English barons against Gaveston.

Due to this action, Gaveston was briefly exiled and Margaret remained fairly unmolested by the upstart until his death in June 1312.