Following the death of his father, Esteban Fernández de Castro, Fernando became Lord of Lemos and Sarria.
He was one of the most powerful and influential nobles of Galicia, like most members of the House of Castro.
In 1304, Fernando took up arms against Ferdinand IV of Castile, by attacking Philip of Castile, who was in Galicia besieging the fortress of Monforte de Lemos.
Fernando's advisers tried to persuade him to reach a peace agreement with the Felipe, who was brother of Violente Sánchez of Castile, his wife.
However, no agreement was reached and Fernando Rodriguez de Castro was killed in the ensuing battle.