- Member of the powerful Galician Castro family. Son of Pedro Fernández de Castro and Isabel Ponce de León.
- Brother of Juana de Castro, Pedro of Castile's second wife, and half-brother of Inês de Castro.
- Was a leader of Pedro of Castile's faction during the civil war between the monarch and his half-brother, the future Enrique II of Castile.
- After Pedro of Castile's death, he continued fighting for his former lord's cause and sought refuge in Portugal.
- One of the clauses of the peace treaty of Santarém, demanded that Fernando de Castro be handed over to Enrique II of Castile, though king Fernando of Portugal found it difficult to fulfill that clause. [Fernando, ch. 84]