Wainwright was appointed to the US Naval Academy in 1864 by President Abraham Lincoln and graduated near the top of his class in 1868. Wainwright's early career is not well documented. From 1890 to 1893 he commanded the, and in 1896 he became the Chief Intelligence Officer of the Navy. In November 1897, he was ordered to the Armored Cruiser, to serve as executive officer under Captain Charles D. Sigsbee.
Spanish–American War
On the night the Maine was blown up in Havana harbor, Wainwright stood beside Sigsbee on the quarterdeck as the vessel was sinking. It was Wainwright who issued the order to lower the lifeboats in which the surviving crew escaped. From the beginning, Wainwright believed the Maine was not blown up by accident and he was impatient to avenge the death of the officers, bluejackets and Marines who died as a result. In the interval between the blowing up of the Maine and the declaration of war against Spain, Wainwright was assigned command of the tender and placed in charge of the salvage survey and recovery of the bodies of the victims. He stayed aboard throughout the seven weeks long Sampson court of inquiry, never setting foot ashore. As the initial salvage closed, for concern about oncoming war, Wainwright remained. On the day that the last salvage team was ordered home, the Spanish naval commander in Havana, Admiral Vincente Manterola, ordered the American flag, which was still flying from the rigging of the wrecked Maine, struck. Wainwright heard of the order and, calling an interpreter, issued an order that immediately made him famous, When Wainwright did finally leave Havana, he hauled down the flag himself. On his arrival in Washington, the U. S. Navy was in the process of purchasing vessels that could be used in the war. Among them was a yacht, the Corsair, owned by J. P. Morgan. She was converted into a gunboat, renamed the, and commissioned with Wainwright in command. In the Battle of Santiago de Cuba he engaged the Spanish torpedo boatsFuror and Plutón, driving them ashore as wrecks with her battery of 6-pounders. The victory came with no casualties, which was attributed to "The accuracy and rapidity of her fire, making the proper service of the guns on the Spanish ships impossible." Wainwright was commended for his valor in this action and was advanced by ten numbers on the promotion seniority list. After ordering his heavily damaged flagship Infanta Maria Teresa to run aground, Spanish fleet commander Spanish Admiral Cervera, was picked up by the Gloucester. Wainwright was there to greet him as he was brought aboard. "I congratulate you, sir," said the American, "on having made as gallant a fight as was ever seen on the sea."
1900-1911
From 1900–1902, Wainwright was Superintendent of United States Naval Academy. During this time, the submarine boat was in Annapolis to train crews for submarines then under construction. Wainwright, having this opportunity to observe their operation, fully endorsed them for their planned harbor defense role. In 1904 he commanded American forces during the Santo Domingo Affair in which his ships shelled rebel troops and supported an amphibious assault. Later, promoted to rear admiral, he commanded the Second Division of the Great White Fleet during that fleet's historic voyage around the world from 1907-1909. Wainwright was invested as a Chevalier of the French Legion of Honor. Retired from active duty on December 7, 1911. Admiral Wainwright died on March 6, 1926 in Washington, D.C. and was interred in Arlington National Cemetery.