Eleanor was born in Castile, now Spain, daughter of Ferdinand III of Castile and Joan, Countess of Ponthieu. Her Castilian name, Leonor, became Alienor or Alianor in England, and Eleanor in modern English. She was named after her great-grandmother, Eleanor of England. Eleanor was the second of five children born to Ferdinand and Joan. Her elder brother Ferdinand was born in 1239/40, her younger brother Louis in 1242/43; two sons born after Louis died young. For the ceremonies in 1291 marking the first anniversary of Eleanor's death, 49 candlebearers were paid to walk in the public procession to commemorate each year of her life. This would date her birth to the year 1241. Since her parents were apart from each other for 13 months while King Ferdinand conducted a military campaign in Andalusia from which he returned to the north of Spain only in February 1241, Eleanor was probably born toward the end of that year. Both the court of her father and her half-brother Alfonso X of Castile were known for its literary atmosphere. Growing up in such an environment probably influenced her later literary activities as queen. She was said to have been at her father's deathbed in Seville in 1252.

Prospective bride to Theobald II of Navarre Eleanor's marriage in 1254 to the future Edward I of England was not the first marriage her family planned for her. The kings of Castile had long made the flimsy claim to be paramount lords of the Kingdom of Navarre in the Pyrenees, and from 1250 Ferdinand III and his heir, Eleanor's half-brother Alfonso X of Castile, hoped she would marry Theobald II of Navarre. To avoid Castilian control, Margaret of Bourbon (mother to Theobald II) in 1252 allied with James I of Aragon instead, and as part of that treaty solemnly promised that Theobald would never marry Eleanor. [edit]Marriage Then, in 1252, Alfonso X resurrected another flimsy ancestral claim, this time to the duchy of Gascony, in the south of Aquitaine, last possession of the Kings of England in France. Henry III of England swiftly countered Alfonso's claims with both diplomatic and military moves. Early in 1254 the two kings began to negotiate; after haggling over the financial provision for Eleanor, Henry and Alfonso agreed she would marry Henry's son Edward, and Alfonso would transfer his Gascon claims to Edward. Henry was so anxious for the marriage to take place that he willingly abandoned elaborate preparations already made for Edward's knighting in England, and agreed that Alfonso would knight Edward before the wedding took place. The young couple married at the monastery of Las Huelgas, Burgos on 1 November 1254. Edward and Eleanor were second cousins once removed, as Eleanor's great-grandmother Eleanor of England was a daughter of King Henry II and Eleanor of Aquitaine. Henry III took pride in resolving the Gascon crisis so decisively, but his English subjects feared that the marriage would bring Eleanor's kinfolk and countrymen to live off Henry's ruinous generosity. Several of her relatives did come to England soon after her marriage. She was too young to stop them or prevent Henry III from paying for them, but she was blamed anyway and her marriage was unpopular. Interestingly enough, Eleanor's mother had been spurned in marriage by Henry III and her great-grandmother, Alys, Countess of the Vexin, had been spurned in marriage by Richard I. However, the presence of more English, Frank and Norman soldiers of fortune and opportunists in the recently reconquered Seville and Cordoba Moorish Kingdoms would be increased, thanks to this alliance between royal houses, until the advent of the later Hundred Years War when it would be symptomatic of extended hostilities between the French and the English for peninsular support.

Prospective bride to Theobald II of Navarre Eleanor's marriage in 1254 to the future Edward I of England was not the first marriage her family planned for her. The kings of Castile had long made the flimsy claim to be paramount lords of the Kingdom of Navarre in the Pyrenees, and from 1250 Ferdinand III and his heir, Eleanor's half-brother Alfonso X of Castile, hoped she would marry Theobald II of Navarre. To avoid Castilian control, Margaret of Bourbon (mother to Theobald II) in 1252 allied with James I of Aragon instead, and as part of that treaty solemnly promised that Theobald would never marry Eleanor. [edit]Marriage Then, in 1252, Alfonso X resurrected another flimsy ancestral claim, this time to the duchy of Gascony, in the south of Aquitaine, last possession of the Kings of England in France. Henry III of England swiftly countered Alfonso's claims with both diplomatic and military moves. Early in 1254 the two kings began to negotiate; after haggling over the financial provision for Eleanor, Henry and Alfonso agreed she would marry Henry's son Edward, and Alfonso would transfer his Gascon claims to Edward. Henry was so anxious for the marriage to take place that he willingly abandoned elaborate preparations already made for Edward's knighting in England, and agreed that Alfonso would knight Edward before the wedding took place. The young couple married at the monastery of Las Huelgas, Burgos on 1 November 1254. Edward and Eleanor were second cousins once removed, as Eleanor's great-grandmother Eleanor of England was a daughter of King Henry II and Eleanor of Aquitaine. Henry III took pride in resolving the Gascon crisis so decisively, but his English subjects feared that the marriage would bring Eleanor's kinfolk and countrymen to live off Henry's ruinous generosity. Several of her relatives did come to England soon after her marriage. She was too young to stop them or prevent Henry III from paying for them, but she was blamed anyway and her marriage was unpopular. Interestingly enough, Eleanor's mother had been spurned in marriage by Henry III and her great-grandmother, Alys, Countess of the Vexin, had been spurned in marriage by Richard I. However, the presence of more English, Frank and Norman soldiers of fortune and opportunists in the recently reconquered Seville and Cordoba Moorish Kingdoms would be increased, thanks to this alliance between royal houses, until the advent of the later Hundred Years War when it would be symptomatic of extended hostilities between the French and the English for peninsular support.

In the autumn of 1290, news reached Edward that Margaret, the Maid of Norway, heiress of Scotland, had died. He had just held a parliament at Clipstone in Nottinghamshire, and continued to linger in those parts, presumably to await news of further developments in Scotland. Eleanor followed him at a leisurely pace as she was unwell with a feverish illness, probably a quartan fever first reported in 1287. After the couple left Clipstone they travelled slowly toward the city of Lincoln, a destination Eleanor would never reach. Her condition worsened when they reached the village of Harby, Nottinghamshire, less than 22 miles (35 km) from Lincoln. The journey was abandoned, and the queen was lodged in the house of Richard de Weston, the foundations of which can still be seen near Harby's parish church. After piously receiving the Church's last rites, she died there on the evening of the 28 November 1290, aged 49 and after 36 years of marriage. Edward was at her bedside to hear her final requests.