Berengaria married King Alfonso IX of León in 1197, but this was annulled in 1204 by Pope Innocent III because they were second cousins. Berengaria and Alfonso had five children, including one who died in infancy, and when she returned to her father's court in Castile, she brought her children with her to Otella.
Berengaria often found herself politically at odds with her former husband. Alfonso had two daughters, Sancha and Dulce, by his first wife, Theresa of Portugal, and wished to disinherit Berengaria's children in favor of these daughters. To this end, he invited John of Brienne to marry his eldest daughter, Sancha, and thus inherit his kingdom. Berengaria sabotaged this plan by convincing John of Brienne to marry her own daughter, Berenguela of León, instead. Later, on 24 September 1230 when Alfonso died, Berengaria and Ferdinand acted to set aside the rights of Sancha and Dulce by offering them a lifetime appanage, which they accepted. This was done so that, with Berengaria's aid, he could assume the Leonese throne.
When her brother Henry died by accident in 1217, Berengaria became sovereign of Castile. She soon renounced her crown in favor of her son Ferdinand. Thereafter she served as the king's motherly advisor; according to the Cronica Latina, her "total intent and desire being to procure honor for her son in every way possible". Berengaria helped quell the rebellious nobles, and then arranged for Ferdinand to marry a high-born wife, Beatrice of Swabia.
Berengaria maintained strong connections with her sister Blanche, who was Queen of France. It was Blanche who suggested sending Jeanne of Ponthieu as a bride for Ferdinand after his first wife's death.
Her children with Alfonso IX included: