Benavides was born in
Granada, the son of Juan Carlos de Benavides Mesía Ponce de León, head of the Inquisition in Cordoba, and of his wife, María Teresa de Medina Liñán y Torres.
 In 1738, he joined the Spanish Army as a cadet, eventually being posted to
Melilla. He became an infantry captain in 1741, a sergeant major in 1754, a lieutenant colonel in 1760 and a full colonel in 1761. On September 25, 1760 he was appointed governor of Puerto Rico by King
Ferdinand VI of Spain.