[3] She served as regent of Spain in the absence of her father Emperor Charles V from 1548 until 1551 and was one of the most powerful empresses of the Holy Roman Empire.

Maria and her brother, Philip, shared similar strong personal views and policies which they retained during the rest of their lives.

While her father was occupied with German affairs, Maria and Maximilian acted as regents of Spain from 1548 to 1551 during the absence of Prince Philip.

She was the patron of the noted Spanish composer Tomás Luis de Victoria, and the great Requiem Mass he wrote in 1603 for her funeral is considered among the best and most refined of his works.

Margaret, the sister of the future Ferdinand II, Holy Roman Emperor, would be one of three women at Philip's court who would apply considerable influence over the king.

Similarly Mariana de San Jose, a favoured nun of Queen Margaret's, was also criticised for her later influence over the king's actions.