At the time of Eleanor's birth at Gloucester, King John's London was in the hands of French forces, John had been forced to sign the Magna Carta and Queen Isabella was in shame. Eleanor never met her father, as he died at Newark Castle when she was barely a year old. The French, led by Prince Louis the Lion, the future Louis VIII, were marching through the south. The only lands loyal to her brother, Henry III of England, were in the Midlands and southwest. The barons ruled the north, but they united with the royalists under William Marshal, 1st Earl of Pembroke, who protected the young king Henry, and Louis was defeated.
Before William the Marshal died in 1219 Eleanor was promised to his son, also named William. They were married on 23 April 1224 at New Temple Church in London. The younger William was 34 and Eleanor only nine. He died in London on 6 April 1231, days before their seventh anniversary. There were no children of this marriage.
Eleanor had brought a dowry of 10 manors and 200 pounds per year to this marriage. According to the law of the time, widows were allowed to retain one third of the estates of the marriage. However, her brother-in-law Richard took all of the estates and sold many, including her dowry, to pay William's debts. Eleanor strove for many years to try and recover her lost property.
The widowed Eleanor swore a holy oath of chastity in the presence of Edmund Rich, Archbishop of Canterbury.
Seven years later, she met Simon de Montfort, 6th Earl of Leicester. According to Matthew Paris, Simon was attracted to Eleanor's beauty and elegance as well as her wealth and high birth. They fell in love and married secretly on 7 January 1238 at the King's chapel in Westminster Palace. Her brother King Henry later alleged that he only allowed the marriage because Simon had seduced Eleanor. The marriage was controversial because of the oath Eleanor had sworn several years before to remain chaste. Because of this, Simon made a pilgrimage to Rome seeking papal approval for their union. Simon and Eleanor had seven children: