Joseph Newton Hemphill was born in Ripley, Ohio on 18 June 1847. He was appointed to the United States Naval Academy on 27 September 1862 from the state of Ohio and graduated in June 1863. On 12 March 1868, Hemphill, who had served the mandatory two year probationary period as a passed naval cadet, received his commission as an ensign in the United States Navy. Hemphill spent the next twenty-five years serving at various shore stations and on numerous ships including: Tacony, Osceola, Monogahela, Kenosha (renamed Plymouth), Tuscarora, Swatara, Powhatan, Constellation, and Jamestown.
In November 1893, Hemphill, now a lieutenant commander (he was promoted to that rank on 26 January 1887), took command of his first ship, the gunboat Fern. He served on that ship until October, 1894 when he was assigned to the Bureau of Yards and Docks, Washington, DC. In August 1898, he was assigned to the auxiliary cruiser Buffalo then fitting out at the Navy Yard, New York and was in command of that ship until July, 1899. After a month of leave, he was assigned to the cruiser Detroit on the North Atlantic Squadron, which he commanded until January 1900. He was a member of the Board of Inspection and Survey from March of that year until May 1902, when he took command of Kearsarge. Hemphill, who had been promoted to Captain on 3 March 1901, remained in command of Kearsarge until April 1904, when he was assigned Chief of Staff, North Atlantic Squadron. He served as Captain of Yard, Navy Yard, New York from June 1904 to August 1906, when he was promoted to Rear Admiral. He was President of the Board of Inspection and Survey from September, 1906 to May 1907 and commanded the Third Squadron, Pacific Fleet from May 1907 to August 1908.
Admiral Hemphill completed his naval service as President of the Naval Examination and Retirement Board and was placed on the Retired List on 18 June 1909. He died in Washington, DC, on 8 July 1931.