He entered Annapolis with the Class of 1879, and he became the first Hispanic-American to graduate from the United States Naval Academy. Lopez served as an ensign aboard the United States Ship Thetis during a voyage of exploration around Alaska in 1888-1889. Lopez Point on Herschel Island was named in his honor by the commander of Thetis, Charles Stockton.
The highlight of his 32-year naval career, was his service under Admiral Dewey"s command at the first major engagement of the Spanish–American War, the Battle of Manila Bay in 1898.
He commanded the destroyer Preble (Doctor of Divinity-12) in 1904–1906. He retired as a Commodore (Rear Admiral) in 1911.
Upon America"s entry into World War I in 1917, Lopez was recalled to duty as acting commandant of the Mare Island Naval Shipyard, located northeast of San Francisco. Commodore Lopez died in Alameda, California after a year"s illness at the age of 77.