From that day Serrano became one of the chief military politicians of Spain. In 1841, he helped Espartero to overthrow the regency of Maria Christina of Bourbon-Sicily. In 1843, at Barcelona he made a "pronunciamiento" against Espartero. He was appointed as the minister of war in the cabinet of Joaquín María López y López, which convoked the Cortes that declared Queen Isabella of age at fifteen. He served in the same capacity in an Olozaga cabinet, sulked as long as the Moderates ("") were in office.