After finishing his studies in 1774, Folch fought in military campaigns in North Africa and the Mediterranean for several years, including the Siege of Melilla (1774–75), the Invasion of Algiers, and the siege of Gibraltar (1780). He was promoted to lieutenant in 1780 and in 1786 he attained the rank of captain. Folch arrived in America in 1780 with the field army ("Ejército de Operaciones") commanded by Victoriano de Navia, and worked his way through the ranks until he was promoted to captain on November 22, 1786. Seven months later, on June 19, 1787, he was appointed commandant of the post at Mobile, where he organized discovery and punitive expeditions against the Maroons. In August 1793, Folch was assigned a naval expedition to map the central part of the west coast of the province of East Florida, the area around Tampa Bay. After successfully completing this arduous task, the governor of Louisiana, Baron Carondelet, appointed him to command two small vessels that he had outfitted to patrol the coast near the mouth of the Mississippi River. Folch performed this service from July, 1794, to July, 1795. On July 28, 1795, Carondelet then appointed Folch the new commandant of the fort of San Fernando de las Barrancas. This was a hardship post at Chickasaw Bluffs overlooking the Mississippi, the present-day site of Memphis, Tennessee. Folch served there until September 1796. He was next assigned duty at Pensacola, where he served as commandant from September 30, 1795, through March 30, 1804. In June 1796 he was appointed governor of West Florida.