She was born in 1292 at Caerphilly in Glamorgan, Wales. She was the eldest daughter of Gilbert de Clare, 6th Earl of Hertford and 7th Earl of Gloucester, and Joan of Acre, daughter of Edward I and Eleanor of Castile; thus she was a granddaughter to Edward I of England. With her sisters, Elizabeth de Clare and Margaret de Clare, she inherited her father's estates after the death of her brother, Gilbert de Clare, 4th Earl of Gloucester at Bannockburn in 1314.
In May 1306 at Westminster, Eleanor married Hugh le Despenser the Younger, the son of Hugh le Despenser, Earl of Winchester and Isabella de Beauchamp, daughter of William de Beauchamp, 9th Earl of Warwick. Her grandfather, King Edward I of England, granted Eleanor a maritagium of 2,000 pounds sterling. Eleanor and Hugh had nine children:
Hugh le Despencer, 2nd Baron le Despencer (1308–1349)
Gilbert le Despenser, (1309–1381).
Edward le Despenser, (1310–1342), soldier, killed at the siege of Vannes;[1] father of Edward le Despencer, 1st Baron le Despencer, Knight of the Garter
John le Despenser, (1311 - June 1366).
Isabel le Despenser (1312–1356), married Richard Fitzalan, 10th Earl of Arundel
Eleanor le Despenser, (c. 1315 - 1351), nun at Sempringham Priory
Joan le Despenser, (c. 1317 - 1384), nun at Shaftesbury Abbey
Margaret le Despenser, (c. 1319 - 1337), nun at Whatton Priory
Elizabeth le Despenser, born 1325, died 13 July 1389, married Maurice de Berkeley, 4th Baron Berkeley.