María was the daughter of the infante Alfonso of Molina and Mayor Alfonso de Menezes. She married her second cousin Sancho IV of Castile in 1282, the second son of Alfonso X the Learned, although the matrimonial dispensation for kinship was not previously granted.
Although the couple was pressured to separate by Rome and others, Sancho chose to honor his wife and delegated many responsibilities to her, including the regency of their son after his death.
Her paternal grandparents were King Alfonso IX of León and Queen Berengaria of Castile. His reign was short since he died in 1295. Through marriage alliances, gifts of territories, and shrewd politics María was able to lead Fernando"s cause to victory, though it did not come easily.
María built her own coalition, relying on the Castilian Cortes to confirm her authority and playing the powerful family clan of Haro against the Lara clan, who supported the opposition.
Civil war continued for several years, and María"s coregent Enrique was often more of an antagonist than a defender of his great-nephew"s cause. Around 1300 the alliance against Fernando began to crumble when one of his principal enemies, Juan Núñez de Lara, was captured and later reconciled to the young king.
Portugal returned to allegiance with Fernando with the promise of a marriage between the Portuguese princess Constanza and the young king of Castile. María de Molina died in Valladolid in 1321.
