Hemphill was born in Athens, Georgia. He attended the University of Georgia (UGA) in Athens where he was a member of the Phi Kappa Literary Society and earned a Bachelor of Arts in 1861. After serving as a Confederate Army colonel in the American Civil War, he went to Atlanta from Athens to teach in 1867, but the next year became business manager to assist his father-in-law, Carey Styles, in founding the pro-secessionist Atlanta Constitution. Styles went broke not able to unload his Albany, Georgia newspaper holdings leaving Hemphill in charge by the next year. His business acumen kept him in charge through many changes including the majority buy-out by Evan Howell.
He began a political life as city councilman-at-large in 1887, the same year he began an unsuccessful banking career. The next few years he served as president of board of education and in 1889 added alderman duties.
While still in control of the Constitution in 1890 he defeated a Black mayoral candidate known now only as "McKinley" and took office the next year.
During his tenure the first building of what became Grady Memorial Hospital was built and a fresh-water pumping station was established on the Chattahoochee River replacing the need for various wells and cisterns (for fires). Part of the 55 acres (220,000 m2) purchased for the associated reservoir included a newly built street named in his honor – Hemphill Ave.
After leaving office, he saw mention of a Cotton Palace in Waco, Texas and suggested what became the Cotton States and International Exposition (1895).
He is buried at Oakland Cemetery in Atlanta.
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|width="30%" align="center" rowspan="1"|Preceded by
John Thomas Glenn |width="40%" style="text-align: center;" rowspan="1"|Mayor of Atlanta
January,1891 – January,1893 |width="30%" align="center" rowspan="1"| Succeeded by
John B. Goodwin |- |}
Template:Mayors of Atlanta
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fr:William A. Hemphill