William was born on the 19th of September 1857, in Philadelphia, Pennsylvania, and he became a midshipman at the age of 15. He graduated from the US Naval Academy five years later and received a commission to Ensign on the 15th of October 1881. William served on two gunboats during the Spanish-American War, the USS Nantucket and Bennington, as well as being on the USS Boston and Albatross.

After the war, he served as the executive officer on board the USS Massachusetts, followed by the USS Albany and commanding the USS Marietta, before being stationed at the Boston Navy Yard and attending the Naval War College. William also travelled to the Philippines and became the captain of the Cavite Navy Yard in February of 1907. Between 1907 and 1914, he commanded seven various classes of vessels, and it was while in command of the USS Florida that he was given command of the landing party once they arrived at Veracruz, Mexico. It was his actions over the two days of fighting that would earn him the Medal of Honor. The citation reads:

For distinguished conduct in battle, engagements of Vera Cruz, 21-22 April 1914. In command of the naval brigade, Capt. Rush was in both days' fighting and almost continually under fire from soon after landing, about noon on the 21st, until we were in possession of the city, about noon of the 22d. His duties required him to be at points of great danger in directing his officers and men, and he exhibited conspicuous courage, coolness and skill in his conduct of the fighting. Upon his courage and skill depended in great measure success or failure. His responsibilities were great, and he met them in a manner worthy of commendation.

William received the Medal of Honor on the 4th of December 1915 and went on to command the Boston Navy Yard. He held this position until he applied for retirement in 1916, but when the US entered World War 1, William was recalled to service and continued to command the Boston Navy Yard until he was relieved of all duty on the 25th of July 1919, after almost 42 years of service.

William was married to Jane in January of 1894 and the couple had one daughter. They retired to Italy, where on the 2nd of August 1940, William Rees Rush died at the age of 82. He is buried with his wife in Arlington National Cemetery: Section 3, Grave 3977.