William Harwar Parker was born in New York City on 8 October 1826, the child, grandchild and ultimately brother of Naval officers. He became a U.S. Navy midshipman in 1841, served in the South Atlantic and, during the Mexican War, was a participant in operations against Veracruz, Tuxpan and Tabasco. Parker graduated in the Naval Academy class of 1847 and was assigned to the sloop of war Yorktown in African waters. In the decade following that ship's loss in 1850, he performed coast survey duties, was an instructor at the Naval Academy, and had sea service aboard USS Cyane in the Caribbean area and in the steam frigates Minnesota and Merrimack in the Far East and the Pacific. He was promoted to the rank of Lieutenant in 1855.

As the Federal Union broke up in 1861, the Parker brothers followed separate paths. Foxhall remained in the U.S. Navy, while William "went south" to join the Virginia Navy and, in June 1861, the Confederate Navy. He commanded the gunboat Beaufort into 1862, taking part in the Roanoke Island battle on 7-8 February 1862 and the actions in Hampton Roads on 8 March and 9 March 1862. In mid-May, he served at Drewry's Bluff when the batteries there were attacked by Union warships.

After several months' shore duty, First Lieutenant Parker was sent to Charleston, S.C., where he was Executive Officer of the ironclad Palmetto State and participated in her attack on Union blockaders in January 1863. In October 1863, he became Superintendent of the Confederate Naval Academy, based on board CSS Patrick Henry in the James River, Virginia. He also commanded the ironclad Richmond. In April 1863, as the Confederate Capital at Richmond, Virginia, was evacuated, he led the Naval Academy's Midshipmen as a guard for their failing Government's archives and treasury.

Following the end of the Civil War, William H. Parker was Captain of a Pacific Mail steamship, served as President of the Maryland Agricultural College, and was Minister to Korea. An accomplished author, he also published several works, among them the generally delightful "Recollections of a Naval Officer 1841-1865". He died in Washington, D.C., on 30 December 1896.